Test InputDecoration API examples

[NobodyForNothing]

Add tests for InputDecoration API example as part of #130459. Updates examples that use the deprecated MaterialState to use WidgetState. Tests files: input_decoration.0.dart, input_decoration.1.dart, input_decoration.2.dart, input_decoration.3.dart, input_decoration.widget_state.0.dart, input_decoration.widget_state.1.dart, input_decoration.prefix_icon_constraints.0.dart, input_decoration.suffix_icon_constraints.0.dart, and input_decoration.label.0.dart

Pre-launch Checklist

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

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[Piinks]

@NobodyForNothing thanks for contributing! It looks like there are some failing checks, can you take a look?

[TahaTesser]

Thanks for the tests collection!

[TahaTesser]

Suggested change

	testWidgets('Is suffix icon', (WidgetTester tester) async {
	testWidgets('Is suffix icon', (WidgetTester tester) async {

Not sure what this means.

[NobodyForNothing]

I changed the description to suffixIcons are placed right of hintText. The goal of this text is to ensure the icon in the example is actually a suffix icon (after content) and not a prefix icon.

While this is not the main point the example is trying to illustrate, I believe it is necessary to differentiate between the prefixIconConstraints and the suffixIconConstraints example.