[ctx_prof] CtxProfAnalysis: populate module data (#102930)

Continuing from #102084, which introduced the analysis, we now populate
it with info about functions contained in the module.

When we will update the profile due to e.g. inlined callsites, we'll
ingest the callee's counters and callsites to the caller. We'll move
those to the caller's respective index space (counter and callers), so
we need to know and maintain where those currently end.

We also don't need to keep profiles not pertinent to this module.

This patch also introduces an arguably much simpler way to track the
GUID of a function from the frontend compilation, through ThinLTO, and
into the post-thinlink compilation step, which doesn't rely on keeping
names around. A separate RFC and patches will discuss extending this to
the current PGO (instrumented and sampled) and other consumers as an
infrastructural component.

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