Rebuild test subsystems

[firelizzard18]

I created this issue to track my work on rebuilding the test explorer and other test subsystems. This work will be done in a separate repository until it is sufficiently complete to merge.

Goals

• Move test discovery out of the extension into gopls.
• Improve code quality and robustness of VSCode's Testing API/provider.
• Unify all test support into a single system.

Non-goals

• Sophisticated subtest discovery. Test and subtest discovery will be handled by gopls instead of the extension, so no further work on the extension will be needed (barring unforeseen issues). Improvements to gopls's subtest discovery will be available as soon as they are released and the user updates gopls.

Tasks

• [x] Implement gopls.modules command
• [x] Implement gopls.packages command
• [x] Add test discovery to gopls.packages
• [x] Implement VSCode's Testing API using gopls for discovery.
• [x] Implement legacy code lenses.
• [x] Improved configurability
  • [x] Include files in the tree.
  • [x] Enable nesting of packages.
  • [x] Disable nesting of subtests.
  • [x] Disable automatic discovery of tests.
• [x] Debug multiple tests (within the same package).
• [x] Support profiling tests/benchmarks.

Nice to have

• [x] Support continuous runs (https://github.com/golang/vscode-go/issues/1952, https://github.com/golang/vscode-go/issues/2483)
• [x] Support files.exclude (https://github.com/golang/vscode-go/issues/1739)
• [ ] Add support for test coverage (https://github.com/golang/vscode-go/issues/3331)
• [ ] Support build tags (https://github.com/golang/vscode-go/issues/1673)
• [ ] Address the backlog of testing issues.

[firelizzard18]

@hyangah VSCode has commands for running tests at the cursor:

And also commands for rerunning the last test run:

It seems like a number of vscode-go's test commands could be deprecated. Maybe for the time being we replace them with calls to the vscode command and show a deprecation notification? WDYT?