[SPIRV] Implement support for SPV_KHR_expect_assume (#66217)

Adds new extension SPV_KHR_expect_assume, new capability
ExpectAssumeKHR as well as the new instructions:
  * OpExpectKHR
  * OpAssumeTrueKHR

These are lowered from respectively llvm.expect.<ty> and llvm.assume
intrinsics.

Previously https://reviews.llvm.org/D157696