Handle private named parameters in field formal conversion assists

[pashaarshad]

Fixes #62436

Updates convert_field_formal_to_normal.dart and convert_to_normal_parameter.dart to properly handle private named parameters.

When converting this._foo to a normal parameter:

• Uses the public name for the parameter (foo)
• Preserves the private field name in the initializer (_foo = foo)
• Only applies when private_named_parameters feature is enabled

[google-cla]

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[mraleph]

@pashaarshad you need to sign CLA, or we can't review the code.

[pashaarshad]

@mraleph Thanks for the reminder. I’ll sign the Google CLA shortly.
Before proceeding, I just want to confirm how to create/sign the CLA and understand whether it’s safe to do so.
Could you please share the steps or a reference link?

[mraleph]

@pashaarshad you can read and sign CLA here: https://cla.developers.google.com/

[copybara-service]

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https://dart-review.googlesource.com/c/sdk/+/475120

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[copybara-service]

https://dart-review.googlesource.com/c/sdk/+/475120 has been updated with the latest commits from this pull request.

[pashaarshad]

@mraleph sir , now i have done the CLA ..................Now check the PR

[mraleph]

I noticed that #62436 is already closed as fixed.

I think @munificent has already landed necessary changes?

[munificent]

Sorry, @pashaarshad, I wasn't aware you were looking at this.

My change handles convert_field_formal_to_normal.dart which this PR also fixes. But this PR also handles convert_to_normal_parameter.dart, which I haven't gotten to yet. (There are so many of these assists and their names are so similar it's hard to keep track. :-/ )

@pashaarshad, do you want to rebase and remove your changes to convert_field_formal_to_normal.dart (and the test) but keep the changes to convert_to_normal_parameter.dart (and its test)?

Then ideally @bwilkerson or @scheglov would review it. Thank you for contributing to Dart!