Add numeric-password variation to TextInputType.numberWithOptions - #190637

Working towards #190204.

Framework companion to the engine/embedding change in #190207.

Summary

Adds a password parameter to TextInputType.numberWithOptions, symmetric to the existing visiblePassword text-class variation.

const TextInputType.numberWithOptions({
  this.signed = false,
  this.decimal = false,
  this.password = false,   // NEW
});

On Android this maps to TYPE_NUMBER_VARIATION_PASSWORD, which the embedding now parses via json.optBoolean("password", false) and ORs into the NUMBER branch of TextInputPlugin.inputTypeFromTextInputType (#190207). It has no effect on iOS, web, or desktop.

password: true declares the platform input classification only. It does not obscure the glyphs Flutter renders — that remains the responsibility of obscureText.

Backward compatibility

• Additive; default false; existing TextInputType.number and numberWithOptions(...) callers are byte-for-byte unchanged.
• JSON is additive — older engines ignore the extra password key.
• No change to obscureText, AutofillHints, or enableIMEPersonalizedLearning semantics.

toJson, operator ==, hashCode, toString, and dartdoc are updated accordingly.

Landing order

Per Tree Hygiene the engine JSON parsing + Android mapping (#190207, merged) lands first; this framework field follows once the engine revision is rolled into the framework.

Pre-launch Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I read the AI contribution guidelines and understand my responsibilities, or I am not using AI tools.
• 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.