Native Input API Improvements and Fixes - #7821

The PR is based on #7815. It fixes multiple issues and incompatibilities, cleans up legacy code design (especially on iOS) and adds a ton of new configuration option.
The PR is best tested over the NativeInputTest class.
The PR fixes #7812.

New NativeInputConfiguration options

• Write Mode: setWriteMode(WriteMode) on NativeInputConfiguration controls how often the in-progress text is mirrored back into the app via TextInputWrapper.writeResults while a native field is open:
  • ONLY_FINAL (default): written once, on close (the previous behavior).
  • TEXT_UPDATES: also on every text change as the IME assembles text; the payload carries the current text plus caret/selection, so the caret is tracked per keystroke.
  • ALL_UPDATES: like TEXT_UPDATES, but also fires on selection/caret-only changes (tap-to-move-caret, drag-select). Not fully functional on iOS < 13.
• Field insets: setHorizontalInsetFraction(float) insets the field from each screen edge. Looks a bit cleaner then edge-to-edge
• Rounded corners: setCornerRadius(float) rounds the TextField corners. Looks better, esp. on iOS
• Text margin: setTextMargin(float) horizontal padding between the field edge and its text.
• Colors: setBackgroundColor / setTextColor / setPlaceholderColor.
• Return key: setReturnKeyType(ReturnKeyType) (GO/SEARCH/SEND/NEXT/DONE). Allows for visual hints what will happen when submitting the input.
• Autofill: setContentType(ContentType) (USERNAME/PASSWORD/NEW_PASSWORD/ONE_TIME_CODE/EMAIL/PHONE). Enables password-manager and OTP autofill.
• Autocapitalization: setAutocapitalization(Autocapitalization) (NONE/WORDS/SENTENCES/CHARACTERS). Allows to independently configure autocapitilization rules.
• Autocomplete threshold: setAutoCompleteThreshold(int) minimum typed characters before suggestions appear.
• Customizer hook: setFieldCustomizer(NativeInputFieldCustomizer), a new public interface for platform-specific tweaks beyond the config (cast the passed object to IOSNativeInput / AndroidNativeInput). Intended for every customization that is not covered yet.

Other changes:

• Built-in validators on Input.InputStringValidator: DIGITAL_VALIDATOR and PHONE_VALIDATOR.
• Better validation: NativeInputConfiguration.validate() now reports all problems at once and additionally checks the current text and every autocomplete entry against the configured validator.

Default appearance change

• The native field now renders inset 5% per side with rounded corners by default (previously edge-to-edge). Restore the old look with setHorizontalInsetFraction(0) and setCornerRadius(0).

iOS / Android fixes

• iOS 26 input-accessory ("Done" pill / liquid-glass) positioning fixed, including the iPad floating keyboard.
• Hardware keyboard on iOS now work properly.
• Better hardware support on android (full compatibility deemed impossible due to missing API's)
• Proper support for iPad floating keyboards.
• Numpad/Phonepad keyboard types now promote to a full keyboard on iPad (they didn't work properly otherwise).
• Multiple autocomplete fixes: proper multiline (UITextView) placeholder, correct positioning, correct handling of the iPad keyboard close button.

Internals & tests

• The iOS and (to a lesser extent) Android native-input backends were restructured where needed to support the above.
• NativeInputTest undergone a significant rewrite to make it easier to use. Heavily assisted by generative AI.