[material_ui] Remove widgets/clipboard_utils.dart imports from date_picker_test.dart, input_date_picker_form_field_test.dart, search_test.dart, selectable_text_test.dart, text_form_field_test.dart, text_selection_test.dart

[QuncCccccc]

Test failures are expected. This PR should land after #12022

Part of flutter/flutter#182636 and flutter/flutter#188395

This PR:

• Removed the cross-import of widgets/clipboard_utils.dart.
• Removed @Skip tag, all tests in this file has passed. semantics_tester.dart has existed in material_ui, so we can directly import semantics_tester.dart;
• Moved the file to test/ folder.

This PR is to port over the changes in flutter/flutter#184278

Pre-Review Checklist

• I read the [Contributor Guide] and followed the process outlined there for submitting PRs.
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• I read the [Tree Hygiene] page, which explains my responsibilities.
• I read and followed the [relevant style guides] and ran [the auto-formatter].
• I signed the [CLA].
• The title of the PR starts with the name of the package surrounded by square brackets, e.g. [shared_preferences]
• I [linked to at least one issue that this PR fixes] in the description above.
• I followed [the version and CHANGELOG instructions], using [semantic versioning] and the [repository CHANGELOG style], or I have commented below to indicate which documented exception this PR falls under[^1].
• I updated/added any relevant documentation (doc comments with ///).
• I added new tests to check the change I am making, or I have commented below to indicate which [test exemption] this PR falls under[^1].
• All existing and new tests are passing.

[gemini-code-assist]

Code Review

This pull request removes the @Skip annotations from multiple test files in packages/material_ui/test/, including date_picker_test.dart, input_date_picker_form_field_test.dart, search_test.dart, selectable_text_test.dart, text_form_field_test.dart, and text_selection_test.dart. Additionally, it updates relative imports to local imports, reorganizes import statements, and wraps asynchronous showDatePicker calls in unawaited within date_picker_test.dart. There are no review comments, and I have no feedback to provide.

[Piinks]

LGTM!