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This fixes https://github.com/flutter/flutter/issues/163627 by trying to
the infer the type of a placeholder on both the template messages and
their localised versions.

This way, if the placeholder is being referenced in the localisation,
but the type is omitted in both the template and the localisation, the
check for if the template and the localisation have the same type will
not fail anymore.

## Pre-launch Checklist

- [x] I read the [Contributor Guide] and followed the process outlined
there for submitting PRs.
- [x] I read the [Tree Hygiene] wiki page, which explains my
responsibilities.
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we expect every widget to implement].
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- [x] I listed at least one issue that this PR fixes in the description
above.
- [x] I updated/added relevant documentation (doc comments with `///`).
- [x] I added new tests to check the change I am making, or this PR is
[test-exempt].
- [x] I followed the [breaking change policy] and added [Data Driven
Fixes] where supported.
- [x] All existing and new tests are passing.

If you need help, consider asking for advice on the #hackers-new channel
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[Flutter Style Guide]:
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[Data Driven Fixes]:
https://github.com/flutter/flutter/blob/main/docs/contributing/Data-driven-Fixes.md



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Co-authored-by: Ben Konyi <bkonyi@google.com>