[profcheck] Require `unknown` metadata have an origin parameter (#157594)

Rather than passes using `!prof = !{!”unknown”}`​for cases where don’t have enough information to emit profile values, this patch captures the pass (or some other information) that can help diagnostics - i.e. `!{!”unknown”, !”some-pass-name”}`​.

For example, suppose we emitted a `select`​ with the unknown metadata, and, later, end up needing to lower that to a conditional branch. If we observe (via sample profiling, for example) that the branch is biased and would have benefitted from a valid profile, the extra information can help speed up debugging.

We can also (in a subsequent pass) generate optimization remarks about such lowered selects, with a similar aim - identify patterns lowering to `select`​ that may be worth some extra investment in extracting a more precise profile.

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