ThemeData minor spring cleaning (flutter#148408)

Do a bit of sprucing up of `ThemeData` in anticipation of future work

Related: flutter#91772

Author: guidezpl

packages/flutter/lib/src/material/theme_data.dart

@@ -136,23 +136,6 @@ abstract class ThemeExtension<T extends ThemeExtension<T>> {
   ThemeExtension<T> lerp(covariant ThemeExtension<T>? other, double t);
 }
 
-// Deriving these values is black magic. The spec claims that pressed buttons
-// have a highlight of 0x66999999, but that's clearly wrong. The videos in the
-// spec show that buttons have a composited highlight of #E1E1E1 on a background
-// of #FAFAFA. Assuming that the highlight really has an opacity of 0x66, we can
-// solve for the actual color of the highlight:
-const Color _kLightThemeHighlightColor = Color(0x66BCBCBC);
-
-// The same video shows the splash compositing to #D7D7D7 on a background of
-// #E1E1E1. Again, assuming the splash has an opacity of 0x66, we can solve for
-// the actual color of the splash:
-const Color _kLightThemeSplashColor = Color(0x66C8C8C8);
-
-// Unfortunately, a similar video isn't available for the dark theme, which
-// means we assume the values in the spec are actually correct.
-const Color _kDarkThemeHighlightColor = Color(0x40CCCCCC);
-const Color _kDarkThemeSplashColor = Color(0x40CCCCCC);
-
 /// Configures the tap target and layout size of certain Material widgets.
 ///
 /// Changing the value in [ThemeData.materialTapTargetSize] will affect the
@@ -262,8 +245,8 @@ class ThemeData with Diagnosticable {
   /// See also:
   ///
   ///  * [ThemeData.from], which creates a ThemeData from a [ColorScheme].
-  ///  * [ThemeData.light], which creates a light blue theme.
-  ///  * [ThemeData.dark], which creates dark theme with a teal secondary [ColorScheme] color.
+  ///  * [ThemeData.light], which creates the default light theme.
+  ///  * [ThemeData.dark], which creates the deafult dark theme.
   ///  * [ColorScheme.fromSeed], which is used to create a [ColorScheme] from a seed color.
   factory ThemeData({
     // For the sanity of the reader, make sure these properties are in the same
@@ -285,14 +268,14 @@ class ThemeData with Diagnosticable {
     bool? useMaterial3,
     VisualDensity? visualDensity,
     // COLOR
-    // [colorScheme] is the preferred way to configure colors. The other color
-    // properties (as well as primarySwatch) will gradually be phased out, see
-    // https://github.com/flutter/flutter/issues/91772.
+    ColorScheme? colorScheme,
     Brightness? brightness,
+    Color? colorSchemeSeed,
+    // [colorScheme] is the preferred way to configure colors. The [Color] properties
+    // listed below (as well as primarySwatch) will gradually be phased out, see
+    // https://github.com/flutter/flutter/issues/91772.
     Color? canvasColor,
     Color? cardColor,
-    ColorScheme? colorScheme,
-    Color? colorSchemeSeed,
     Color? dialogBackgroundColor,
     Color? disabledColor,
     Color? dividerColor,
@@ -365,6 +348,7 @@ class ThemeData with Diagnosticable {
     TimePickerThemeData? timePickerTheme,
     ToggleButtonsThemeData? toggleButtonsTheme,
     TooltipThemeData? tooltipTheme,
+    // DEPRECATED (newest deprecations at the bottom)
     @Deprecated(
       'Use OverflowBar instead. '
       'This feature was deprecated after v3.21.0-10.0.pre.',
@@ -471,8 +455,8 @@ class ThemeData with Diagnosticable {
       materialTapTargetSize: materialTapTargetSize,
     );
     disabledColor ??= isDark ? Colors.white38 : Colors.black38;
-    highlightColor ??= isDark ? _kDarkThemeHighlightColor : _kLightThemeHighlightColor;
-    splashColor ??= isDark ? _kDarkThemeSplashColor : _kLightThemeSplashColor;
+    highlightColor ??= isDark ? const Color(0x40CCCCCC) : const Color(0x66BCBCBC);
+    splashColor ??= isDark ? const Color(0x40CCCCCC) : const Color(0x66C8C8C8);
 
     // TYPOGRAPHY & ICONOGRAPHY
     typography ??= useMaterial3
@@ -666,12 +650,12 @@ class ThemeData with Diagnosticable {
     required this.useMaterial3,
     required this.visualDensity,
     // COLOR
-    // [colorScheme] is the preferred way to configure colors. The other color
-    // properties will gradually be phased out, see
+    required this.colorScheme,
+    // [colorScheme] is the preferred way to configure colors. The [Color] properties
+    // listed below (as well as primarySwatch) will gradually be phased out, see
     // https://github.com/flutter/flutter/issues/91772.
     required this.canvasColor,
     required this.cardColor,
-    required this.colorScheme,
     required this.dialogBackgroundColor,
     required this.disabledColor,
     required this.dividerColor,
@@ -749,7 +733,6 @@ class ThemeData with Diagnosticable {
   }) : // DEPRECATED (newest deprecations at the bottom)
        // should not be `required`, use getter pattern to avoid breakages.
        _buttonBarTheme = buttonBarTheme,
-        // DEPRECATED (newest deprecations at the bottom)
        assert(buttonBarTheme != null);
 
   /// Create a [ThemeData] based on the colors in the given [colorScheme] and
@@ -1432,13 +1415,13 @@ class ThemeData with Diagnosticable {
     InteractiveInkFeatureFactory? splashFactory,
     VisualDensity? visualDensity,
     // COLOR
-    // [colorScheme] is the preferred way to configure colors. The other color
-    // properties will gradually be phased out, see
-    // https://github.com/flutter/flutter/issues/91772.
+    ColorScheme? colorScheme,
     Brightness? brightness,
+    // [colorScheme] is the preferred way to configure colors. The [Color] properties
+    // listed below (as well as primarySwatch) will gradually be phased out, see
+    // https://github.com/flutter/flutter/issues/91772.
     Color? canvasColor,
     Color? cardColor,
-    ColorScheme? colorScheme,
     Color? dialogBackgroundColor,
     Color? disabledColor,
     Color? dividerColor,