* Clean up mouse region code

* remove even more code

* copied over changes from

* copied over changes from

* a193f08cd [fuchsia] Switch from core-jit to core snapshots. (flutter/engine#30744)

* 7e504629e Roll Skia from b21c4af0f670 to 759bc62a06d2 (3 revisions) (flutter/engine#30848)

* 8db50380d Remove usages of deprecated setSystemUiVisibility() (flutter/engine#29493)

* c05d0dfd2 Roll Skia from 759bc62a06d2 to 455e580b9c78 (2 revisions) (flutter/engine#30849)

* 1fab2fb21 Roll Dart SDK from f1c98a571d1a to b36d861d5487 (1 revision) (flutter/engine#30850)

* f9385e7d5 Remove unused field initializing formal parameters. (flutter/engine#30822)

* b6e5d999c Roll buildroot to 7effd69. (flutter/engine#30851)

* 742eaf886 Roll Skia from 455e580b9c78 to c505bdca9d60 (1 revision) (flutter/engine#30852)

* d0f2bebbb Don't retain the MTLTexture or MTLDevice in TestMetalContext (flutter/engine#30832)

* f121c1fe6 Create a DisplayList benchmarks dylib on iOS (flutter/engine#30833)

* 449979776 Roll Skia from c505bdca9d60 to 62b32180c192 (1 revision) (flutter/engine#30855)

* fcf745805 Move SoftwareCanvasProvider into its own source file (flutter/engine#30856)

* 794a833a1 Roll Fuchsia Mac SDK from Uvw9UoGSm... to BQ2l2096A... (flutter/engine#30859)

* 4b32e1c48 Roll Skia from 62b32180c192 to 119fb6bb2568 (1 revision) (flutter/engine#30860)

* facfa743e Roll Dart SDK from b36d861d5487 to ba044d5e9c03 (1 revision) (flutter/engine#30861)

* f6613c9d5 Roll Skia from 119fb6bb2568 to 7c80b2f08ead (1 revision) (flutter/engine#30862)

* fb3ee7f2b Ensure that PlatformViewIOS does not call into Shell semantics APIs during destruction (flutter/engine#30835)

* 073e6c5d3 [Windows, Keyboard] Lift key event redispatching to KeyboardManagerWin32 (flutter/engine#30702)

* 88e67a2cf Roll Skia from 7c80b2f08ead to a6f2ebf30fea (1 revision) (flutter/engine#30863)

* 1f4e7fa19 Roll Dart SDK from ba044d5e9c03 to aa6fbac07951 (1 revision) (flutter/engine#30867)

* 3fbd42762 Roll Skia from a6f2ebf30fea to 76e62d32d979 (1 revision) (flutter/engine#30868)

* b6db081f4 Roll Skia from 76e62d32d979 to 7aec4b164e79 (1 revision) (flutter/engine#30869)

* b92fd27d4 Roll Dart SDK from aa6fbac07951 to 68ccd13498be (1 revision) (flutter/engine#30870)

* 896136680 Roll Dart SDK from 68ccd13498be to dcab0d0b2f6c (1 revision) (flutter/engine#30872)

* 18ea2ce56 Roll Skia from 7aec4b164e79 to dd9e165ef7d0 (1 revision) (flutter/engine#30874)

* 9d660d9a9 Roll Fuchsia Mac SDK from BQ2l2096A... to bGW3xlB1D... (flutter/engine#30875)

* ad68b1b61 Roll Skia from dd9e165ef7d0 to 1f0e64acd621 (1 revision) (flutter/engine#30876)

* b61a6f5ab [fuchsia] stamp package with target api level (flutter/engine#30857)

* 57874896c Roll Skia from 1f0e64acd621 to f260a297c68d (1 revision) (flutter/engine#30877)

* 87ba2d8cf Roll Dart SDK from dcab0d0b2f6c to d0d4dbfc6e69 (1 revision) (flutter/engine#30878)

* 83d99a580 Roll Fuchsia Linux SDK from 35I2K_Bou... to V541xkYVr... (flutter/engine#30879)

* 50adf4c1f Revert "Remove usages of deprecated setSystemUiVisibility()" (flutter/engine#30880)

This reverts commit a3fd36a1.

This extracts the examples that are in flutter/engine@main/lib/ui/text.dart into examples in the examples/api/lib/ui directory and adds some simple tests for them.

Also, fixes some inconsistent test file naming.

This is step 1: the next step is to remove the examples from the dart:ui code.

Before this change, it was possible to select and copy obscured text from a text field.

This  changes things so that:
- Obscured text fields don't allow copy or cut.
- If a field is both obscured and read-only, then selection is disabled as well (if you can't modify it, and can't copy it, there's no point in selecting it).

This adds a simple example to CustomMultiChildLayout that lays out colored containers in a cascade.

This reverts commit e78f135f.

* Modularize ReorderableListView auto scrolling logic

* comment

* fix test

* addressing comment