Add "clang-tidy --fix" flag to automatically apply fixes

[jmagman]

Similar to ci/format.sh --fix, add a ci/lint.sh --fix to automatically apply fixes suggested by clang-tidy.

When I run ci/lint.sh --fix locally I see changes applied:
Example:

engine/flow/display_list.cc

Line 111 in ddf4bd5

SetStyleOp(SkPaint::Style style) : style(style) {}

-  SetStyleOp(SkPaint::Style style) : style(style) {}
+  explicit SetStyleOp(SkPaint::Style style) : style(style) {}

engine/shell/platform/darwin/common/framework/Source/FlutterCodecs.mm

Line 13 in 138c91c

_sharedInstance = [FlutterBinaryCodec new];

-    _sharedInstance = [FlutterBinaryCodec new];
+    _sharedInstance = [[FlutterBinaryCodec alloc] init];

Pre-launch Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I read the Tree Hygiene wiki page, which explains my responsibilities.
• I read and followed the Flutter Style Guide and the C++, Objective-C, Java style guides.
• I listed at least one issue that this PR fixes in the description above.
• I added new tests to check the change I am making or feature I am adding, or Hixie said the PR is test-exempt. See testing the engine for instructions on
  writing and running engine tests.
• I updated/added relevant documentation (doc comments with ///).
• I signed the CLA.
• All existing and new tests are passing.

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