doc: document the --with-perfetto build flag

[lazerg]

The perfetto tracing support added in #64565 was never documented, so there is
no way to find out from the docs that the --with-perfetto configure flag
exists or what it changes.

This adds a short BUILDING.md section for the flag. The trace events and CLI
docs do not name the configure flag. They only describe how a perfetto build
behaves: traces come out as perfetto protobuf, the default trace file name
becomes node_trace.${rotation}.pftrace, and JSON output and inspector-based
collection are not available.

Fixes: #65055

[nodejs-github-bot]

Review requested:

• @nodejs/build
• @nodejs/tsc

[avivkeller]

We usually don't document configure flags in doc/api, only in the non-user facing docs

[lazerg]

I checked doc/api before changing this. A few files there do name configure flags. intl.md has an "Options for building Node.js" section with --with-intl and --with-icu-default-data-dir, including ./configure examples. dtls.md says the module must be enabled at build time with the --experimental-dtls configure flag. ffi.md names --shared-ffi, and crypto.md shows ./configure --openssl-conf-name=<name>.

cli.md is different though. It never names a configure flag anywhere. It describes the build condition by its effect instead, like "only available in builds with FFI support" for --experimental-ffi. My line was the only exception in that file, so you are right about it.

I pushed a change that keeps --with-perfetto in BUILDING.md only. cli.md and tracing.md now say "builds with Perfetto support" and link to BUILDING.md for the flag itself.

I kept the behavior text. --trace-event-file-pattern really does default to a different extension in such a build, and NodeTracing is not registered. That is runtime behavior an API reader can hit, so it seemed worth keeping in doc/api. Happy to drop it if you still think it belongs only in BUILDING.md.