LintDiff feedback at Preview

* [ ] Look at improving [checkout performance](https://github.com/Azure/azure-rest-api-specs/pull/32697#pullrequestreview-2635067799)
* [x] Use JS helpers, contribute where appropriate ([comment](https://github.com/Azure/azure-rest-api-specs/pull/32697#discussion_r1966563546), [comment](https://github.com/Azure/azure-rest-api-specs/pull/32697#pullrequestreview-2635093812), [comment](https://github.com/Azure/azure-rest-api-specs/pull/32697#pullrequestreview-2635092011), [comment](https://github.com/Azure/azure-rest-api-specs/pull/32697/files#r2001851663))
* [x] Consider porting shareable code to JS-only implementation (may need simplification) ([comment](https://github.com/Azure/azure-rest-api-specs/pull/32697#discussion_r1966564485))
* [x] Ensure [dependency alignment in eng/tools/lint-diff/package.json](https://github.com/Azure/azure-rest-api-specs/pull/32697#discussion_r2001849250)
* [x] Use [exec.js instead of runChecks.ts:executeCommand](https://github.com/Azure/azure-rest-api-specs/pull/32697#discussion_r2001854459)
* [x] Standardize on marked and yaml for markdown and yaml parsing ([comment](https://github.com/Azure/azure-rest-api-specs/pull/32697/files#r2001848368))
* [x] Platform-specific tests (deal with path separators properly)
* [x] On failure, generate output table text
* [x] On exit, generate link to summary so the user can see the markdown output
* [ ] Consider moving validator into the repo so we don't have to sync it from npm

Overall by file:

* lint-diff.ts -- argument parsing can be cleaned up/simplified
* processChanges.ts -- Most/all should be in a helper under .github/src, hopefully this can be simplified with a single graph creation/traversal
* markdown-utils.ts -- Same as processChanges.ts: Move it to .github/src
* runChecks.ts -- Use the common JS `exec` helper
* util.ts -- Most can go in a .github/src helper