## Problem 1
In #124852 we added chrome for mac
version to provisioning list. Since then the version was not updated
because it's not added to platforms covered by automation.

## Problem 2
In #129851 we manually upgraded v8
version. The next automated PR
#129934 downgraded it.

## Changes
- Add mac to automated version check
- Add mac smoke tests running only on the automated bump PRs, following
the pattern used in library tests on mac.
- Automated update can be only an upgrade: always check if the new value
> old value.

## Problem

WASM perf runs (and other V8 shell-engine legs) abort at startup:

```
Warning: unknown flag --experimental-wasm-exnref.
MONO_WASM: Assert failed: This browser/engine doesn't support WASM exception handling.
main.mjs: Error: Top-level await promise never resolved
```

## Root cause

- #129851 (`[browser] WASM exception handling to use the standardized
exnref`) switched the runtime to the **exnref** exception-handling
proposal, which requires a V8 that understands
`--experimental-wasm-exnref` (V8 15.1+). That PR set
`linux/macos/win_V8Version` to `15.1.103`.
- The later automated chrome-for-testing bump #129934 recomputed the V8
version from the pinned Chrome (149 → V8 14.9) and **reverted**
`linux_V8Version` and `win_V8Version` back to `14.9.207` (leaving only
`macos_V8Version` at `15.1.103`).

`14.9.207` predates exnref, so it rejects the flag and the runtime's
startup feature check (`featureWasmFinalEh`) asserts. The wasm perf leg
is hit because [`dotnet/performance`
`run_performance_job.py`](https://github.com/dotnet/performance/blob/main/scripts/run_performance_job.py)
reads `linux_V8Version` and installs exactly that build via `jsvu`.

## Fix

Restore `linux_V8Version` and `win_V8Version` to `15.1.103` (matching
`macos_V8Version`). The `v8-linux64-rel-15.1.103.zip` and
`v8-win32-rel-15.1.103.zip` binaries exist on the V8 canary CDN that
`jsvu` / `DownloadAndInstallV8` use (verified 200 OK), and `15.1.103`
supports exnref behind the `--experimental-wasm-exnref` flag already
emitted by `eng/testing/WasmRunnerTemplate.sh` and the perf harness
(dotnet/performance#5247).

## Note on the auto-updater

The chrome-for-testing auto-bump derives the V8 version from the Chrome
milestone, so a future run will revert this to `14.9.x` again unless the
pinned Chrome is advanced to a milestone whose V8 is 15.1+ (Chrome 151)
or the updater is taught not to downgrade V8 below the exnref floor.
Tracking: #129849.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>