[Android] Remove old `InputType` constructor from embedding (#191244)

Working towards #190204.

Follow-up to #190207.

## Summary

Removes the 3-arg convenience constructor `InputType(type, isSigned,
isDecimal)` from `TextInputChannel.InputType`. Since #190207 added
`isPassword`, the canonical constructor is the 4-arg one; the 3-arg
overload only remained for compatibility with existing test call sites,
which are now migrated to the 4-arg form with `isPassword = false`. This
matches `Configuration`, which keeps a single canonical constructor.

No production callers remain — `InputType.fromJson` was already the only
construction path in the embedding.

## Test Plan

- Existing `TextInputPluginTest` / `TextInputChannelTest` pass unchanged
in behavior (matrix tests already cover `isPassword` separately).
- Verified locally that both changed files compile against the embedding
classpath.

Co-authored-by: Camille Simon <43054281+camsim99@users.noreply.github.com>