[Bug]: JSON reporter emits a separate spec per project when testDir is not the current directory

Finding: In Playwright Test 1.64.0 on Node 22.22.0 and Ubuntu 24.04 (as reported), running npx playwright test --reporter=json from the project root with testDir set to ./tests and two projects (chromium, firefox) reportedly yields one spec per project instead of one merged spec holding both projects' tests ([issue #43266](https://github.com/microsoft/playwright/issues/43266)). Reported behavior: The reporter's config uses testDir './tests' and two projects, with a single trivial test file. From the project root the JSON output lists the 'has title' spec twice, once with chromium and once with firefox. Tests inside test.describe are duplicated the same way. The reporter states that the same config run from inside tests/ with -c .. gives the expected single spec containing both projects. The reporter concludes that the report shape depends on the directory the command is run from ([issue #43266](https://github.com/microsoft/playwright/issues/43266)). Suspected cause (hypothesis, not confirmed): The reporter says _mergeTestsFromSuite in packages/playwright/src/reporters/json.ts matches specs with s.file === toPosixPath(path.relative(rootDir, spec.file)). The reporter says spec.file is already relative to rootDir, so path.relative resolves it against process.cwd(), and the comparison only succeeds when cwd equals rootDir. The reporter also says suites in the same function are matched with _locationMatches, which would work for specs too, and that the behavior seems to date back to 1.27, when the comparison switched from the absolute test.location.file to the relative spec.file. All of this is the reporter's own analysis; no maintainer has confirmed it ([issue #43266](https://github.com/microsoft/playwright/issues/43266)). KFA inference (not in the source): Tools that post-process the JSON output, for example by grouping by spec title, could see different structures depending on the working directory if the reported behavior holds. This is an inference and was not checked. Workaround status: The issue body does not propose a workaround. The reporter gives the inside-tests/ command (cd tests && npx playwright test -c .. --reporter=json) only as the comparison showing the expected output, stated as [["has title",["chromium","firefox"]]]. KFA has not verified it, and it is not a confirmed workaround ([issue #43266](https://github.com/microsoft/playwright/issues/43266)). Status: At the time of the supplied data the issue is open with no comments, no maintainer response, no linked fix commit and no released fix. The reporter offers to send a PR with a regression test in tests/playwright-test/reporter-json.spec.ts, but no PR was supplied. Limitation: This is a single external report. It was not reproduced by KFA, and comment coverage was unavailable because of an HTTPError, so later discussion may exist that was not seen.