This enables support for atomic RMW ops (add, sub, min and max to be
precise) with `bfloat16` operands, via the [SPV_INTEL_16bit_atomics
extension](https://github.com/intel/llvm/pull/20009). It's logically a
successor to #166031 (I should've used a stack), but I'm putting it up
for early review.

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Co-authored-by: Matt Arsenault <arsenm2@gmail.com>

--Added support for the extension SPV_ALTERA_blocking_pipes
--Added test files for the extension SPV_ALTERA_blocking_pipes

Enable the `SPV_INTEL_bfloat16_arithmetic` extension, which allows arithmetic, relational and `OpExtInst` instructions to take `bfloat16` arguments. This patch only adds support to arithmetic and relational ops. The extension itself is rather fresh, but `bfloat16` is ubiquitous at this point and not supporting these ops is limiting.

This adds BE support for the
[`SPV_INTEL_kernel_attributes`](https://github.khronos.org/SPIRV-Registry/extensions/INTEL/SPV_INTEL_kernel_attributes.html)
extension. The extension is necessary to encode the rather useful
`max_work_group_size` kernel attribute, via `OpExecutionMode
MaxWorkgroupSizeINTEL`, which is the only Execution Mode added by the
extension that this patch adds full processing for. Future patches will
add the other Execution Modes and Capabilities. The test is adapted from
the equivalent Translator test; it depends on #165815.

Implement maximal reconvergence in SPIR-V codegen.

Addresses https://github.com/llvm/llvm-project/issues/136930

This PR introduces the support for the SPIR-V extension
`SPV_INTEL_predicated_io`. This extension adds predicated load and store
instructions. Predicated load performs load from memory if predicate is
true; otherwise, it uses default_value as a result. Predicated store
performs store of value to memory if predicate is true; otherwise, it
does nothing.

Reference Specification:

https://github.com/intel/llvm/blob/sycl/sycl/doc/design/spirv-extensions/SPV_INTEL_predicated_io.asciidoc

Added support for the extension to support more storageclass for printf
strings.

This PR introduces the support for the SPIR-V extension
`SPV_KHR_bfloat16`. This extension extends the `OpTypeFloat` instruction
to enable the use of bfloat16 types with cooperative matrices and dot
products.

TODO:
Per the `SPV_KHR_bfloat16` extension, there are a limited number of
instructions that can use the bfloat16 type. For example, arithmetic
instructions like `FAdd` or `FMul` can't operate on `bfloat16` values.
Therefore, a future patch should be added to either emit an error or
fall back to FP32 for arithmetic in cases where bfloat16 must not be
used.

Reference Specification:

https://github.com/KhronosGroup/SPIRV-Registry/blob/main/extensions/KHR/SPV_KHR_bfloat16.asciidoc

We can pass a range to llvm::is_contained.

The default behaviour in DXC is to allow all extesions the compiler
knows about. We did the same in clang: all extensions that clang knows
about. However, this causes the shader to use different extensions
because the two compilers have different sets of extensions.

To avoid using a new extension when moving from DXC to Clang, we add the
special DXC suboptions to `-fspv-extension`. If `-fspv-extension=DXC` is
used, then the available extensions will be those available in DXC.

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Co-authored-by: Chris B <beanz@abolishcrlf.org>