[wasm][debugger][tests] Allow overriding which browser to use (#19769)

[wasm][debugger][tests] Allow overriding which browser to use (#19769)

* [wasm][debugger] Reduce debugger-tests timeout to 40m

- And run that before the system tests since the debugger is more likely
to fail at this point.

Based on @lewing's suggestion

* [wasm][tests] Allow overriding which browser to use

.. via the envvar `WASM_TESTS_ChromePath`.

This can also be set in an `appsettings.json` file next to the test
binaries, like:
```
{ "ChromePath": "</path/to/chrome/binary>" }
```

Also, prefer stable Chrome over Canary.

Co-authored by @lewing