Add coverage support for fuzzing_regression_test

[zhenyudg]

Adds support for bazel coverage to gather coverage on fuzz targets replayed on the corpus.

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[zhenyudg]

@googlebot I signed it!

[fmeum]

@zhenyudg Are you still planning to work on this PR? I have a concrete need for this feature now and would thus like to pick it up soon.

[zhenyudg]

@fmeum Pardon the radio silence on the MR. I'm on leave until October 3, and I would be more than happy if you can pick this up.

[zhenyudg]

Superseded by https://github.com/bazelbuild/rules_fuzzing/pull/212