add positron.r.interpreters.exclude setting to exclude R installation paths

[sharon-wang]

Summary

• addresses R: configure inclusion/exclusion of runtimes #6205
• adds a new setting positron.r.interpreters.exclude which allows the user to specify R installation binary paths or directories containing R installations that should be excluded from the UI in Positron

Settings UI

Settings JSON

    "positron.r.interpreters.exclude": [
        "/opt/local"
    ]

R Language Pack Output

...
2025-02-25 10:11:26.178 [info] User-specified R binaries:
[
  "/opt/local/R/4.3-arm64/Resources/bin/R"
]
...
2025-02-25 10:11:26.178 [info] Candidate R binary at /opt/local/R/4.3-arm64/Resources/bin/R
2025-02-25 10:11:26.178 [info] User-specified R installation paths to exclude:
[
  "/opt/local"
]
2025-02-25 10:11:26.178 [info] User has excluded R installation at /opt/local/R/4.3-arm64/Resources/bin/R
2025-02-25 10:11:26.178 [info] R installation discovered: {
  "usable": false,
  "supported": true,
  "reasonDiscovered": [
    "User-specified location",
    "Found in a conventional location for R binaries installed on a server"
  ],
  "reasonRejected": "Installation path was excluded via settings",
  "binpath": "/opt/local/R/4.3-arm64/Resources/bin/R",
  "homepath": "/Library/Frameworks/R.framework/Versions/4.3-arm64/Resources",
  "semVersion": {
    "options": {},
    "loose": false,
    "includePrerelease": false,
    "raw": "4.3.3",
    "major": 4,
    "minor": 3,
    "patch": 3,
    "prerelease": [],
    "build": [],
    "version": "4.3.3"
  },
  "version": "4.3.3",
  "arch": "arm64",
  "current": false,
  "orthogonal": true
}
...
2025-02-25 10:11:26.178 [info] Filtering out /opt/local/R/4.3-arm64/Resources/bin/R, reason: Installation path was excluded via settings.
2025-02-25 10:11:26.178 [warning] Some discovered R installations are unusable by Positron.
2025-02-25 10:11:26.178 [warning] Learn more about R discovery at https://positron.posit.co/r-installations

Release Notes

New Features

• New setting to exclude R installation paths from the UI (R: configure inclusion/exclusion of runtimes #6205)

Bug Fixes

• N/A

QA Notes

• please test with and without the positron.r.customBinaries and positron.r.customRootFolders settings which allow "includes" to be specified
  • see https://positron.posit.co/r-installations.html#customizing-r-discovery for more info on these options
• Positron will need to be restarted upon changing the settings so that discovery can re-run with the settings applied
• excluding interpreters via positron.r.interpreters.exclude will take precedence over includes with positron.r.customBinaries or positron.r.customRootFolders
• Relative paths specified in the options are ignored

[github-actions]

E2E Tests 🚀
This PR will run tests tagged with: @:critical

^{readme  valid tags}

[jennybc]

LGTM

I didn't delve deeply into the implementation, since it looks like the path utilities are ported from elsewhere. Mostly just some comments on naming and describing things.

[melissa-barca]

LGTM!

[sharon-wang]

MacOS CI issues will be resolved in #6496.