browser-integration-tests: port request and web vitals suites to span streaming #24143

Follow the porting recipe in the parent issue.

http.client and resource span names are low cardinality under streaming, and web vitals arrive as standalone streamed spans rather than as measurements on a transaction. Expect assertion shape changes, not just helper swaps.

Suites

• tracing/request/* (25 pinned files)
• tracing/metrics/* (11 pinned files, web vitals and resource spans)
• tracing/interactions/*
• tracing/user-timing/*

Twins to fold back

• tracing/request: fetch-streamed, xhr-streamed, fetch-relative-url-streamed, xhr-relative-url-streamed, fetch-streamed-track-stream-performance
• tracing/metrics: web-vitals-lcp-streamed-spans, web-vitals-cls-streamed-spans, web-vitals-inp-streamed-spans, web-vitals-ttfb-streamed, pageload-resource-spans-streamed