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.

This patch moves the check if any vector instructions will be generated
from getInstructionCost to be based on VPlan. This simplifies
getInstructionCost, is more accurate as we check the final result and
also allows us to exit early once we visit a recipe that generates
vector instructions.

The helper can then be re-used by the VPlan-based cost model to match
the legacy selectVectorizationFactor behavior, this fixing a crash and
paving the way to recommit
https://github.com/llvm/llvm-project/pull/92555.

PR: https://github.com/llvm/llvm-project/pull/96622

Regenerate test checks to better show impact of
https://github.com/llvm/llvm-project/pull/96622.

A set of microbenchmarks (https://github.com/llvm/llvm-test-suite/pull/26) showed that loop interleaving can be beneficial for loops with low trip count as well. Loop interleaving count computation is updated accordingly in prior patches while this patch removes the loop trip count threshold for interleaving. 

This reverts commit 14e3450fb57305aa9ff3e9e60687b458e43835c9.

This reverts commit 0d748b4d32cbddf58a1ff83f3ff178ec1ad49edc.
This is causing some failures when building Spec2017 with scalable
vectors. Reverting to investigate.