Make the WinDbg/TTD version a setting instead of downloading the latest (Fix #1130) - #1140

…latest (Fix #1130)

The latest WinDbg release (1.2606.22001.0) crashes the DbgEng TTD adapter on
stop (#1129). The installer now downloads a pinned version (1.2603.20001.0)
directly by URL, and falls back to the latest version via the appinstaller
manifest if the pinned download fails.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Since we install a pinned WinDbg version rather than the latest release, there is
nothing to check online. The latest-version query was reduced to returning a
compile-time constant, but it still went through a background thread, an FFI call
and a subprocess that spawned the installer CLI to parse its JSON output.

Worse, the check itself became wrong: IsVersionUpToDate() compared with >=, so a
user who already had the broken 1.2606.22001.0 installed - exactly the population
hit by #1129/#1130 - was told they were up to date and never offered the fix.

Remove GetLatestVersion(), IsVersionUpToDate() and CompareVersions() from the
installer library, the check-update CLI command and its exit code 2, the
core/FFI/API GetLatestVersion() plumbing along with the now-unused subprocess and
JSON helpers, and the dialog's async version fetch.

The pinned version moves to windbg_version.h so the UI can display it directly.
The dialog now compares the installed version against that constant and offers
Reinstall when they match and Install when they do not - not Update, since
replacing a newer WinDbg with the validated one is a downgrade.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

…nload

The earlier commits on this branch pinned the version in a header but still kept the
old "download whatever Microsoft released last" path around as a fallback, which is a
lot of code for a path we do not want taken.

Replace both with a single `debugger.windbgVersion` setting:

- the installer takes `--windbg-version <ver>` and builds the MSIX bundle URL directly
  from it, defaulting to `kDefaultVersion` in the new installer/windbg_version.h
- the core passes the setting's value when it launches the installer, so a different
  released version can be installed without a new build
- the appinstaller manifest download, XML parsing and version comparison are gone,
  along with the `check-update` command and the `GetWinDbgLatestVersion` FFI/API
- the dialog compares the installed version against the setting instead of querying
  Microsoft in a background thread

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>