This patch fixes a couple of places where memprof-related metadata
(!memprof and !callsite) were being dropped, and one place where PGO
metadata (!prof) was being dropped.

All were due to instances of combineMetadata() being invoked. That
function drops all metadata not in the list provided by the client, and
also drops any not in its switch statement.

Memprof metadata needed a case in the combineMetadata switch statement.
For now we simply keep the metadata of the instruction being kept, which
doesn't retain all the profile information when two calls with
memprof metadata are being combined, but at least retains some.

For the memprof metadata being dropped during call CSE, add memprof and
callsite metadata to the list of known ids in combineMetadataForCSE.

Neither memprof nor regular prof metadata were in the list of known ids
for the callsite in MemCpyOptimizer, which was added to combine AA
metadata after optimization of byval arguments fed by memcpy
instructions, and similar types of optimizations of memcpy uses.

There is one other callsite of combineMetadata, but it is only invoked
on load instructions, which do not carry these types of metadata.

The compiler crashes with an ICE when it tries to create a `memset` with
scalable size.

When a memmove happens to clobber source data, and such data have
been previously memset'd, the memmove may be redundant.

I'd like to use the name CaptureInfo to represent the new attribute
proposed at
https://discourse.llvm.org/t/rfc-improvements-to-capture-tracking/81420,
but it's already taken by AA, and I can't think of great alternatives
(CaptureEffects would be something of a stretch).

As such, I'd like to rename CaptureInfo -> CaptureAnalysis in AA, which
also seems like the more accurate terminology.

Identified with misc-include-cleaner.

Rename the function to reflect its correct behavior and to be consistent
with `Module::getOrInsertFunction`. This is also in preparation of
adding a new `Intrinsic::getDeclaration` that will have behavior similar
to `Module::getFunction` (i.e, just lookup, no creation).

Pass EarliestEscapeInfo to BatchAA in MemCpyOpt. This allows memcpy
elimination in cases where one of the involved pointers is captured
after the relevant memcpy/call.

Everything else in this method using BatchAA, apart from this
call.

Fix a long-standing TODO.