experiment: special tracing view for API testing

[Skn0tt]

In #19177, lots of folks are asking for improvements to debugging API Tests. We show pretty much all they ask for in the UI, but a lot of the screen space is taken up by browser-specific UI that's simply irrelevant to API testing. This PR demonstrates what a special-purpose "API Testing View" could look like. Instead of the snapshot viewer, it shows request details front-and-center, and it hides the inspector and console tabs.

[github-actions]

Test results for "tests 1"

9 failed
❌ [chromium-library] › library/trace-viewer.spec.ts:900:1 › should open two trace files
❌ [chromium-library] › library/trace-viewer.spec.ts:900:1 › should open two trace files
❌ [chromium-library] › library/client-certificates.spec.ts:237:3 › fetch › should fail with matching certificates in legacy pfx format
❌ [chromium-library] › library/client-certificates.spec.ts:602:3 › browser › should fail with matching certificates in legacy pfx format
❌ [chromium-library] › library/trace-viewer.spec.ts:900:1 › should open two trace files
❌ [firefox-library] › library/trace-viewer.spec.ts:900:1 › should open two trace files
❌ [chromium-library] › library/trace-viewer.spec.ts:900:1 › should open two trace files
❌ [playwright-test] › babel.spec.ts:135:5 › should not transform external
❌ [webkit-library] › library/trace-viewer.spec.ts:900:1 › should open two trace files

35492 passed, 659 skipped
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Merge workflow run.