[CP] Workaround iOS text input crash for emoji+Korean text

[jmagman]

Hot fixing: flutter/flutter#111494
PR: #36295 and #34508

CP issue: flutter/flutter#112963

#36621 plus cherry pick #34508

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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[skia-gold]

Gold has detected about 1 new digest(s) on patchset 2.
View them at https://flutter-engine-gold.skia.org/cl/github/36807

[jmagman]

The tests pass on this PR https://ci.chromium.org/p/flutter/builders/try/Mac%20Unopt/19879.

[cyanglaz]

LGTM

[jmagman]

@godofredoc this is good to merge now, release is a go!

[godofredoc]

@godofredoc this is good to merge now, release is a go!

Awesome, thanks!