[vivekjm]

Summary

Fixes #4829.

This changes the IconButton ripple content from flexGrow: 1 to flex: 1 so the pressable content reliably fills the fixed-size container before centering the icon. That keeps the icon centered when callers add custom container styles such as a background color.

Test plan

• yarn test src/components/__tests__/IconButton.test.tsx --runInBand
• yarn lint
• yarn typecheck
• yarn test -u updated snapshots affected by the shared IconButton style. The full run otherwise passes except src/babel/__tests__/index.js, which cannot start because this checkout does not have lib/mappings.json generated and yarn generate-mappings points to a missing scripts/generate-mappings.ts file.

[Doberjohn]

Thanks for this fix, @vivekjm. We'd like to merge it before the IconButton rewrite in #5103. Could you bring the branch up to date with main? Most of the conflicts are snapshots, which yarn test -u regenerates. On main, components no longer pass test IDs down by default (#5088, #5099), so the new test may need to find the button by role instead. Once it's updated I'll approve the CI run and review it.