Introduced the convergent equivalent of the existing G_INTRINSIC opcodes:

- G_INTRINSIC_CONVERGENT
- G_INTRINSIC_CONVERGENT_W_SIDE_EFFECTS

Out of the targets that currently have some support for GlobalISel, the patch
assumes that the convergent intrinsics only relevant to SPIRV and AMDGPU.

Reviewed By: arsenm

Differential Revision: https://reviews.llvm.org/D154766

With C++17 there is no Clang pedantic warning or MSVC C5051.

Identified with modernize-use-default-member-init.

This also adds new interfaces for the fixed- and scalable case:
* LLT::fixed_vector
* LLT::scalable_vector

The strategy for migrating to the new interfaces was as follows:
* If the new LLT is a (modified) clone of another LLT, taking the
  same number of elements, then use LLT::vector(OtherTy.getElementCount())
  or if the number of elements is halfed/doubled, it uses .divideCoefficientBy(2)
  or operator*. That is because there is no reason to specifically restrict
  the types to 'fixed_vector'.
* If the algorithm works on the number of elements (as unsigned), then
  just use fixed_vector. This will need to be fixed up in the future when
  modifying the algorithm to also work for scalable vectors, and will need
  then need additional tests to confirm the behaviour works the same for
  scalable vectors.
* If the test used the '/*Scalable=*/true` flag of LLT::vector, then
  this is replaced by LLT::scalable_vector.

Reviewed By: aemerson

Differential Revision: https://reviews.llvm.org/D104451

My local compiler was fine with it but the bots complain about ambiguous types.

It's still in use in a few places so we can't delete it yet but there's not
many at this point.

Differential Revision: https://reviews.llvm.org/D103352