Emit low cardinality request handler span names #23533

Ensure request handler spans emit low-cardinality span names when span streaming is enabled.

Span name rules: https://getsentry.github.io/sentry-conventions/names/#resource-resources

Fallback constant: REQUEST_HANDLER_SPAN_NAME_FALLBACK in packages/core/src/tracing/spans/spanNames.ts

Part of #22350 — remember to check traceLifecycle and keep the existing name for static mode.

Note: the @see link on this constant in spanNames.ts points at the resource section, which looks like a copy-paste leftover — worth double-checking against the conventions for the correct request handler section.