Handle external dependencies

[cwahbong]

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Seems the current plugin implementation does not handle the external dependencies well: when specify "Query Expression" in configuration like: @repo//..., the tree explorer, coverage, and the quick pick is not showing the dependencies from external dependencies. This makes some workspaces that's organized in assembling local_repository rules not working.

I already have several local workaround fixes for this, but it would be better to also append the test cases for better coverage and prevent regressions for existing users..

• [x] Coverage: handle the generated report path's SF:external/<repo>/.... entries.
• [ ] Ｑuick picks: replace hard coded queries like //...:* or //...) to query expressions. Not sure if we have to use separate query for packages and targets.
• [ ] Code lens: still exploring / surveying. Seems we have to map the BUILD files back to @repo//path:BUILD, which is a opposite direction to those mapping in tree explorer and coverage.
• [ ] Tree explorer:
  • [ ] Replace hard coded queries to query expression.
  • [ ] Make the grouping handles the package name starting with @<repo>//.