debug: Debug Configuration tests failing on release branch

[hyangah]

This is v0.33.0 release blocker and needs to be fixed.

cc @suzmue @polinasok

 3 failing
 1) Debug Configuration Merge User Settings
      merge 'go' config from settings.json
        default settings are applied:

     AssertionError [ERR_ASSERTION]: Expected values to be strictly equal:
+ actual - expected

+ 'legacy'
- 'dlv-dap'
     + expected - actual

     -legacy
     +dlv-dap
     
 	at Context.<anonymous> (out/test/integration/goDebugConfiguration.test.js:183:20)

 2) Debug Configuration Default DebugAdapter
      default debugAdapter should be 'dlv-dap':

     AssertionError [ERR_ASSERTION]: Expected values to be strictly equal:
+ actual - expected

+ 'legacy'
- 'dlv-dap'
     + expected - actual

     -legacy
     +dlv-dap
     
 	at Context.<anonymous> (out/test/integration/goDebugConfiguration.test.js:731:16)

 3) Debug Configuration Default DebugAdapter
      default debugAdapter for remote mode should be 'legacy' when not in Preview mode:

     AssertionError [ERR_ASSERTION]: Expected values to be strictly equal:
+ actual - expected

+ 'dlv-dap'
- 'legacy'
     + expected - actual

     -dlv-dap
     +legacy
     
 	at Context.<anonymous> (out/test/integration/goDebugConfiguration.test.js:745:16)

Error: 3 tests failed.
   at /workspace/out/test/integration/index.js:58:27
   at done (/workspace/node_modules/mocha/lib/mocha.js:1068:7)
   at processTicksAndRejections (node:internal/process/task_queues:96:5)
[main 2022-04-25T22:03:12.498Z] Extension host with pid 356 exited with code: 1, signal: null.
Exit code:   1
Done

[gopherbot]

Change https://go.dev/cl/402215 mentions this issue: [release] Revert "src/goDebugConfiguration: default to dlv-dap for remote in preview mode"

[gopherbot]

Change https://go.dev/cl/402220 mentions this issue: src/goDebugConfiguration: fix debugAdapter default selection

[polinasok]

I looked more into the issue with extensionInfo potentially not being initialized in test mode. I can't see it ddirectly in the debugger stopped in a test, but I can see it if I copy things over to a local variable or print to console. It changes when I manually change preview manually in package.json.

That said, it might be a better approach to stub it out (the way it is done with getGoConfig) instead of relying on the release vs non-release environment for running CI or manually changing package.json for testing. This way we can test both modes.