[Arul1998]

Fixes #33978.

Problem

writeValue skipped re-formatting the input when the incoming value was the same as the current one. This was added in #32447 and #32485 to work around signal forms writing the same value back into the CVA while the user was typing (#32442, #32475).

As a side effect, an unparseable value could no longer be cleared programmatically. After the user types something like foo, the model value is null, so reset() / setValue(null) calls writeValue(null) with the value that's already there and gets skipped. The invalid text stays in the input, and because _lastValueValid is reset, no matDatepickerParse error is shown either. Signal forms reset() goes through the same path and is affected as well.

Fix

Angular 22.0.0 deduplicates writeValue calls in the CVA interop (angular/angular@2e9aeea0f), and @angular/material 22 requires @angular/core ^22.0.0, so the workaround is no longer needed. This PR removes it so writeValue always re-formats the input, and drops the now-unused reformat parameter from _assignValueProgrammatically.

Tests

• Replaced the two reactive forms specs that simulated the old signal forms loopback (and asserted the text is kept) with a spec that reset() clears invalid text.
• Added signal forms specs using the real [formField] integration:
  • invalid text is not cleared while typing (bug(Datepicker): Input form with signal forms deletes the field too aggressively #32475)
  • a valid date is not re-formatted while typing (bug(Datepicker): with signal forms the input field automatically interprets incomplete data during input, thereby hindering/preventing input #32442)
  • reset() clears invalid text

I also checked it manually in an Angular / Material 22.2.3 app, before and after patching:

Scenario	Before	After
Reactive forms: type foo, then reset()	foo stays	cleared
Reactive forms: type bar, then setValue(null)	bar stays	cleared
Signal forms: type foo, then reset()	foo stays	cleared
Signal forms: type foo	kept	kept
Signal forms: type 1 → 1/ → … → 1/1/2026	not clobbered	not clobbered
Signal forms with debounce: same typing sequences	not clobbered	not clobbered
Programmatic valid date (reactive and signal)	formatted	formatted