New assist to add/edit `hide` at import for ambiguous import

[FMorschel]

This PR adds a new assist to add/update hide to imports when ambiguous_import is triggered.

Related to https://github.com/dart-lang/sdk/issues/56830.

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[FMorschel]

Requested @bwilkerson to review on Gerrit, as he wrote the options list to fix ambiguous_import.

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