perf(core): use a reverse lookup in forgetTransientResolutions

[merceyz]

What's the problem this PR addresses?

When Project.forgetResolution is called with a locator it loops over Project.storedResolutions to find all descriptors that point to that locator, this becomes expensive when called multiple times, which Project.forgetTransientResolutions potentially does.

How did you fix it?

Create a reverse mapping of Project.storedResolutions to efficiently lookup all descriptors pointing to a locator and delete them directly in Project.forgetTransientResolutions.

Results

Tested on the DefinitelyTyped repo with its 8629 workspaces (matching only types/*):

$ YARN_IGNORE_PATH=1 hyperfine -w 1 "node ./after.cjs --mode skip-build" "node ./before.cjs --mode skip-build"
Benchmark 1: node ./after.cjs --mode skip-build
  Time (mean ± σ):     15.802 s ±  0.437 s    [User: 12.243 s, System: 10.097 s]
  Range (min … max):   14.979 s … 16.265 s    10 runs

Benchmark 2: node ./before.cjs --mode skip-build
  Time (mean ± σ):     17.260 s ±  0.471 s    [User: 13.692 s, System: 9.957 s]
  Range (min … max):   16.425 s … 18.000 s    10 runs

Summary
  'node ./after.cjs --mode skip-build' ran
    1.09 ± 0.04 times faster than 'node ./before.cjs --mode skip-build'

Checklist

• I have read the Contributing Guide.
• I have set the packages that need to be released for my changes to be effective.
• I will check that all automated PR checks pass before the PR gets reviewed.