fix(@angular-devkit/build-angular): remove double-watch in karma

[jkrems]

The Karma file watching was racing with the file writes done by the application builder. Since we already tell Karma when to reun via .refeshFiles(), disabling Karma's own file watcher should make things more reliable.

This allows removing a weird special-case in the test case and removes the noisy "File chaned" logs generated by Karma.

Fixes #28755

[jkrems]

Increased the debounce window in the test which shouldn't fundamentally slow the test down. The race between Karma starting to run, the watching build, and the browser running tests may not be worth fixing since it likely requires larger refactoring. Which may end up ugly unless we change Karma as well (and I'm pretty sure we don't want to do that at this point).

Boo. Need to look more into this, it still doesn't appear to be passing consistently on CI.

[jkrems]

The end result is a bit more complex now, mostly to remove a race condition that caused the test instability:

1. The initial build completes.
2. During the initial watching build, a file is modified.
3. The file change is never picked up - there are no further builds and the test cannot make progress.

This is likely not a super common case for real users but correctness-wise, it's likely better to set up the file watching at the very beginning. Doing so requires reusing the same buildApplicationInternal call for the entire test run which makes for ugly code (manual iterator loop instead of a neat for await ... of).

P.S.: Looks like the tests are passing now. Requested re-review because the majority of changed lines is now different than what was originally reviewed.

[jkrems]

The changes were merged into the following branches: main, 19.0.x

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