[IR] Convert from nocapture to captures(none) (#123181)

This PR removes the old `nocapture` attribute, replacing it with the new
`captures` attribute introduced in #116990. This change is
intended

[IR] Convert from nocapture to captures(none) (#123181)

This PR removes the old `nocapture` attribute, replacing it with the new
`captures` attribute introduced in #116990. This change is
intended to be essentially NFC, replacing existing uses of `nocapture`
with `captures(none)` without adding any new analysis capabilities.
Making use of non-`none` values is left for a followup.

Some notes:
* `nocapture` will be upgraded to `captures(none)` by the bitcode
reader.
* `nocapture` will also be upgraded by the textual IR reader. This is to
make it easier to use old IR files and somewhat reduce the test churn in
this PR.
* Helper APIs like `doesNotCapture()` will check for `captures(none)`.
* MLIR import will convert `captures(none)` into an `llvm.nocapture`
attribute. The representation in the LLVM IR dialect should be updated
separately.

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InferAddressSpaces: Improve handling of instructions with multiple pointer uses (#101922)

The use list iteration worked correctly for the load and store case. The atomic
instructions happen to have

InferAddressSpaces: Improve handling of instructions with multiple pointer uses (#101922)

The use list iteration worked correctly for the load and store case. The atomic
instructions happen to have the pointer value as the last visited operand, but we
rejected the instruction as simple after the first encountered use.

Ignore the use list for the recognized load/store/atomic instructions, and just
try to directly replace the known pointer use.

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InferAddressSpaces: Fix mishandling stores of pointers to themselves (#101877)