feat(@angular-devkit/build-angular): Switch to karma-coverage

[kyliau]

This commit switches coverage tooling from karma-coverage-istanbul-reporter
to karma-coverage since it's better supported.

Fixes #17757

[kyliau]

Because the coverage test is run asynchronously in a "runaway" promise, I had to do two things here to make the tests work:

1. Call setTimeout to wait for coverage files to be written
2. Pass Karma results to the callback because the callback is immediately invoked even though the test hasn't actually completed. Passing the Karma results by reference allows us to retrieve the final exit code modified by karma-coverage if the coverage doesn't meet the threshold.

I'm not very satisfied with both approaches, but after discussing with @filipesilva I think this is the best compromise.
I'm totally happy to revise this PR if there are better suggestions.

[alan-agius4]

With this change, it means that currently with the CLI, there is no way to exit the process with a non zero error code when code coverage threshold is not met.

[alan-agius4]

This looks great.

Left a couple of comments.

Also, currently code-coverage in the console we display a summary, however it seems that it doesn't work with the new plugin. Can you take a look?

TOTAL: 3 SUCCESS
TOTAL: 3 SUCCESS
TOTAL: 3 SUCCESS

=============================== Coverage summary ===============================
Statements   : 88.89% ( 8/9 )
Branches     : 100% ( 0/0 )
Functions    : 100% ( 0/0 )
Lines        : 85.71% ( 6/7 )
================================================================================

[kyliau]

Update: even though karma-coverage 2.0.3 was released to address the issue of onRunComplete() return a promise, more changes are needed upstream before this could be implemented on CLI side without hacky solutions. This is currently blocked on:

1. fix(reporter): set exit code when thresholds aren't met karma-runner/karma-coverage#420
2. feat(server): allow 'exit' listeners to set exit code karma-runner/karma#3541

Since karma-coverage 2.0.3 no longer modifies the karma results in-place, the solution implemented in this PR is no longer applicable.

[alan-agius4]

@kyliau, any chance to get in touch with one of the Karma Googler’s to prioritise the above fixes?

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[alan-agius4]

@googlebot I consent

[googlebot]

CLAs look good, thanks!

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[alan-agius4]

LGTM, just one small NIT.

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