proposal: expose build meta info to runtime

[utrack]

Piggybacking off #35667

Build info (runtime/debug.modinfo,runtime.buildVersion, go.metadata, etc) can be useful if exposed to runtime.
For example, access to a list of module versions and their SHA-1s would allow people to expose it via some HTTP handler, so monitoring would pick it up and signal if there's a service running with some dependency that has critical bugs in it.

[utrack]

Welp, somehow I've overlooked debug.ReadBuildInfo. Go version can be pulled via runtime.Version, so only ldflags are missing - guess they'll be accessible when #35667 is out.