[Impeller] make default glyph atlas size much bigger. (#52787)

Now that we no longer have a full CPU copy of the glyph atlas, it should be cheaper to make a larger initial atlas to reduce churn from resizing seen in applications like flutter/flutter#138798

Requires #52746

Author: Jonah Williams

impeller/typographer/backends/skia/typographer_context_skia.cc

@@ -194,16 +194,12 @@ static ISize OptimumAtlasSizeForFontGlyphPairs(
     const std::vector<FontGlyphPair>& pairs,
     std::vector<Rect>& glyph_positions,
     const std::shared_ptr<GlyphAtlasContext>& atlas_context,
-    GlyphAtlas::Type type,
     const ISize& max_texture_size) {
-  static constexpr auto kMinAtlasSize = 8u;
-  static constexpr auto kMinAlphaBitmapSize = 1024u;
+  static constexpr ISize kMinAtlasSize = ISize{4096, 1024};
 
   TRACE_EVENT0("impeller", __FUNCTION__);
 
-  ISize current_size = type == GlyphAtlas::Type::kAlphaBitmap
-                           ? ISize(kMinAlphaBitmapSize, kMinAlphaBitmapSize)
-                           : ISize(kMinAtlasSize, kMinAtlasSize);
+  ISize current_size = kMinAtlasSize;
   size_t total_pairs = pairs.size() + 1;
   do {
     auto rect_packer = std::shared_ptr<RectanglePacker>(
@@ -406,7 +402,6 @@ std::shared_ptr<GlyphAtlas> TypographerContextSkia::CreateGlyphAtlas(
       font_glyph_pairs,                                             //
       glyph_positions,                                              //
       atlas_context,                                                //
-      type,                                                         //
       context.GetResourceAllocator()->GetMaxTextureSizeSupported()  //
   );
 

impeller/typographer/typographer_unittests.cc

@@ -151,8 +151,8 @@ TEST_P(TypographerTest, GlyphAtlasWithOddUniqueGlyphSize) {
   ASSERT_NE(atlas, nullptr);
   ASSERT_NE(atlas->GetTexture(), nullptr);
 
-  ASSERT_EQ(atlas->GetTexture()->GetSize().width,
-            atlas->GetTexture()->GetSize().height);
+  EXPECT_EQ(atlas->GetTexture()->GetSize().width, 4096u);
+  EXPECT_EQ(atlas->GetTexture()->GetSize().height, 1024u);
 }
 
 TEST_P(TypographerTest, GlyphAtlasIsRecycledIfUnchanged) {