[CP] [cfe] Fix Field.isCovariantByClass for fields without implicit setters

[alexmarkov]

Commit(s) to merge

0263371

Target

stable

Prepared changelist for beta/stable

https://dart-review.googlesource.com/c/sdk/+/399624

Issue Description

CFE was incorrectly marking a final field in a constant as covariant, which caused crash in TFA during AOT and dart2wasm compilation.

What is the fix

CFE no longer marks fields without implicit setters as covariant.

Why cherry-pick

No easy workaround.

Risk

Low.

Issue link(s)

#57084, flutter/flutter#159760

Extra Info

Should be included into the upcoming Flutter stable release.

[alexmarkov]

/cc @johnniwinther @mraleph

[dart-github-bot]

Summary: Incorrect covariance marking of final fields in constants caused crashes in AOT and dart2wasm. The fix prevents this by not marking fields without implicit setters as covariant.

[johnniwinther]

LGTM