Migrate to WidgetStateInputBorder (#176386)

Follow up https://github.com/flutter/flutter/pull/176330

Migrate the remaining files from `MaterialStateOutlineInputBorder` and
`MaterialStateUnderlineInputBorder ` to `WidgetStateInputBorder `. This
PR only focus on `WidgetStateInputBorder`.

- This minimizes conflicts and reduces the size of the PR for easier
reviews and follow up
- I'll work on the other elements of
`packages/flutter/lib/src/material/material_state.dart` into other PRs

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we expect every widget to implement].
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- [ ] I listed at least one issue that this PR fixes in the description
above.
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[test-exempt].
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Fixes] where supported.
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packages/flutter/lib/src/material/input_decorator.dart

@@ -5261,9 +5261,9 @@ class InputDecorationThemeData with Diagnosticable {
 
   /// The shape of the border to draw around the decoration's container.
   ///
-  /// If [border] is a [MaterialStateUnderlineInputBorder]
-  /// or [MaterialStateOutlineInputBorder], then the effective border can depend on
-  /// the [WidgetState.focused] state, i.e. if the [TextField] is focused or not.
+  /// If [border] is a [WidgetStateInputBorder], then the effective border can
+  /// depend on the [WidgetState.focused] state, i.e. if the [TextField] is
+  /// focused or not.
   ///
   /// The decoration's container is the area which is filled if [filled] is
   /// true and bordered per the [border]. It's the area adjacent to

packages/flutter/test/material/input_decorator_test.dart

@@ -8456,7 +8456,7 @@ void main() {
     );
 
     // InputDecoration (baseDecoration) defines InputDecoration properties
-    final MaterialStateOutlineInputBorder border = MaterialStateOutlineInputBorder.resolveWith((
+    final WidgetStateInputBorder border = WidgetStateInputBorder.resolveWith((
       Set<WidgetState> states,
     ) {
       return const OutlineInputBorder();
@@ -8522,7 +8522,7 @@ void main() {
     expect(decoration.counterStyle, decorationStyle);
     expect(decoration.filled, false);
     expect(decoration.fillColor, Colors.blue);
-    expect(decoration.border, isA<MaterialStateOutlineInputBorder>());
+    expect(decoration.border, isA<WidgetStateInputBorder>());
     expect(decoration.alignLabelWithHint, false);
     expect(
       decoration.constraints,