Add some retry around browser launching (dart-lang#1676)

Towards dart-lang#1578

Recursively attempt to launch the browser on the first few timeouts
before throwing the ApplicationException.

Restore previous timeout of 30 seconds.
The 45 second timeout was mainly to investigate whether extra time would
resolve flakes. It didn't seem to help at all and it doesn't seem likely
that even more time would help. Go back to 30 seconds to reduce the pain
of hitting retries (though it will still be painful).

release test_core 0.4.11 and test 1.20.1 (dart-lang#1651)

release test_core 0.4.11 and test 1.20.1 (dart-lang#1651)

revert test_core dep

fix parsing of windows file paths into a URI (dart-lang#1611)

dart-lang#1614

fix parsing of windows file paths into a URI (dart-lang#1611)

dart-lang#1614

release all packages (dart-lang#1608)

release all packages (dart-lang#1608)