[ci] Update repo for 3.50 stable release - #13628

Does the flutter/core-packages steps of
[Updating-Packages-repo-for-a-stable-release.md](https://github.com/flutter/flutter/blob/main/docs/ecosystem/release/Updating-Packages-repo-for-a-stable-release.md#fluttercore-packages)
for the 3.50 stable release. This repo wasn't updated for 3.47, so this
also catches up on that release:

- Updates the multi-version analysis and test matrix to the Dart
versions of flutter/packages' stable, N-1, and N-2 Flutter versions:
3.14.0 (Flutter 3.50.0), 3.13.7 (Flutter 3.47.9), and 3.12.2 (Flutter
3.44.9), plus `main`. The matrix previously covered only N-1 and stable;
this adds N-2 as the doc describes.
- Updates the Windows unit tests and the release action to Dart 3.14.0.
- Raises `min_dart` to 3.12.0 (the Dart version of Flutter 3.44.0,
flutter/packages' new minimum), and updates all packages with
`update-min-sdk --flutter-min=3.44.0`, run with the repo tooling from
flutter/packages#13628, which has the updated version mapping.
- Adds `NEXT` CHANGELOG entries with `update-release-info
--version=next` (no version bumps, per repo policy).

Additional adjustments needed for CI with the updated versions:

- Applies `dart fix --code=prefer_initializing_formals` in
`multicast_dns` and `mustache_template`, whose language version moved to
Dart 3.12, adopting private named parameters (`this._foo`; call-site
argument names are unchanged).
- Also removes the outdated "we aren't actually testing N-1 or N-2" note
from the `min_dart` comment in `.repo_tool_config.yaml`, since the
matrix now covers N-1 and N-2.

Companion to flutter/packages#13628.

There's no tracking issue for this routine post-release update.

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…r#196450)

flutter/packages@653628e...14f9933

2026-11-12 [email protected] [material_ui]
Fix SnackBarThemeData.lerp dropping showCloseIcon
(flutter/packages#13449)
2026-11-11 [email protected] [ci] Update repo
for 3.50 stable release (flutter/packages#13628)
2026-11-11 [email protected] [vector_graphics]
Use font-family lists as a family with fallbacks
(flutter/packages#13552)
2026-11-11 [email protected] Roll Flutter (stable) from
c197ca5 to ab29120 (1647 revisions) (flutter/packages#13625)
2026-11-11 [email protected] [shared_prferences] Adopts
mockito-kotlin in tests (flutter/packages#13624)
2026-11-11 [email protected] [cupertino_ui] Dim disabled
CupertinoSlider controls (flutter/packages#13419)
2026-11-11 [email protected] [flutter_svg] Invalidate pending cache
entries on clear and evict (flutter/packages#13595)
2026-11-11 [email protected] [cupertino_ui] Fix the tinted
button's fill opacity (flutter/packages#13436)
2026-11-11 [email protected] [various]
Support SVG filters (blur, offset, feMerge) (flutter/packages#11909)

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