feat(Pressable): add support for PlatformColor and alpha

[adrcotfas]

Summary:

android_ripple on Pressable (and TouchableNativeFeedback.Ripple()) only
accepted numeric (pre-processed ARGB int) colors. Passing a PlatformColor
would throw an invariant in JS, making it impossible to use theme-aware colors for the ripple effect.

This PR fixes two separate guards that blocked PlatformColor:

1. JS (useAndroidRippleForView.js): removed the invariant that
   rejected non-numeric processed colors.
2. C++ (NativeDrawable.h): switched from hasType<int32_t>() to the
   shared fromRawValue pipeline (same path used by every other color prop),
   which resolves PlatformColor objects via JNI.

A new alpha: number (0–1) field is also added so users can apply opacity to
a PlatformColor whose value is fully opaque and can't have alpha embedded at
the JS level.

Unresolvable PlatformColor resources are handled gracefully: on New Arch,
C++ detects UndefinedColor and omits the color key so Kotlin falls back to
colorControlHighlight; on Old Arch, ReactDrawableHelper catches the
JSApplicationCausedNativeException and falls back to colorControlHighlight
instead of crashing.

Changelog:

[ANDROID] [ADDED] - android_ripple now accepts PlatformColor for
theme-aware ripple colors, and a new alpha (0–1) parameter for controlling
ripple opacity independently of the color value.

Test Plan:

Automated:

• Existing Pressable snapshot tests pass unchanged.
• Updated snapshot for PlatformColor + alpha to use ?attr/colorAccent
  (matching the RNTester example).
• Added snapshot test should not crash with an unresolvable PlatformColor
  verifying the component renders at the JS level without throwing.

Manual (RNTester → Pressable → "Pressable with PlatformColor ripple and alpha"):

1. PlatformColor('?attr/colorAccent'), no alpha → full-opacity accent ripple
2. PlatformColor('?attr/colorAccent'), alpha=0.3 → 30% opacity accent ripple
3. #FF0000, no alpha → full red ripple (regression check)
4. #FF0000, alpha=0.5 → 50% opacity red ripple
5. Toggle system light/dark mode → ripple color updates (PlatformColor cache
   invalidation works)
6. Pass an intentionally invalid attribute (e.g. ?attr/doesNotExist) → no
   crash, ripple falls back to default colorControlHighlight grey

Pressable_PlatformColor_alpha.webm

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