MC Descriptor Range Representation currently depend on Object
structures. This PR removes that dependency and in order to facilitate
removing to_underlying usage in follow-up PRs.

This pr implements support for a root signature as a target, as specified
[here](https://github.com/llvm/wg-hlsl/blob/main/proposals/0029-root-signature-driver-options.md#target-root-signature-version).

This is implemented in the following steps:
1. Add `rootsignature` as a shader model environment type and define
`rootsig` as a `target_profile`. Only valid as versions 1.0 and 1.1
2. Updates `HLSLFrontendAction` to invoke a special handling of
constructing the `ASTContext` if we are considering an `hlsl` file and
with a `rootsignature` target
3. Defines the special handling to minimally instantiate the `Parser`
and `Sema` to insert the `RootSignatureDecl`
4. Updates `CGHLSLRuntime` to emit the constructed root signature decl
as part of `dx.rootsignatures` with a `null` entry function
5. Updates `DXILRootSignature` to handle emitting a root signature
without an entry function
6. Updates `ToolChains/HLSL` to invoke `only-section=RTS0` to strip any
other generated information

Resolves: https://github.com/llvm/llvm-project/issues/150286.

##### Implementation Considerations
Ideally we could invoke this as part of `clang-dxc` without the need of
a source file. However, the initialization of the `Parser` and `Lexer`
becomes quite complicated to handle this.

Technically, we could avoid generating any of the extra information that
is removed in step 6. However, it seems better to re-use the logic in
`llvm-objcopy` without any need for additional custom logic in
`DXILRootSignature`.

Removes uniformity bit from resource initialization intrinsics `llvm.{dx|spv}.resource.handlefrombinding` and `llvm.{dx|spv}.resource.handlefromimplicitbinding`. The flag currently always set to `false`. It should be derived from resource analysis and not provided by codegen.

Closes #135452

This pr fixes some inconsistencies in behaviour of how we handle
`StaticSamplersOffset` with respect to DXC and `RootParameterOffset`.
Namely:

1. Make codegen of `RTS0` always compute the `StaticSamplersOffset`
regardless if there are any `StaticSampler`s. This is to be consistent
and produce an identical `DXContainer` as DXC.
2. Make the `StaticSamplersOffset` and `RootParametersOffset` optional
parameters in the yaml description. This means it will be used when it
is specified (which was not necassarily the case before).
3. Enforce that the provided `StaticSamplersOffset` and
`RootParametersOffset` in a yaml description match the computed value.

For more context see:
https://github.com/llvm/llvm-project/issues/155299.

Description of existing test updates updates:
- `CodeGen/DirectX/ContainerData`: Updated to codegen computed values
(previously unspecified)
- `llvm-objcopy/DXContainer`: Updated to `yaml2obj` computed values
(previously unspecified)
- `ObjectYAML/DXContainer`: Updated to `yaml2obj` computed values
(previously incorrect)
- `ObjectYAML/DXContainerYAMLTest`: Updated to `yaml2obj` computed
values (previously incorrect)

See newly added tests for testing of optional parameter functionality
and `StaticSamplersOffset` computation.

Resolves: https://github.com/llvm/llvm-project/issues/155299

This patch is refactoring Root Parameter Header in DX Container backend
to remove the usage of `to_underlying`. This requires some changes:
first, MC Root Signature should not depend on Object/DXContainer.h;
Second, we need to assume data to be valid in scenarios where it was
originally not expected, this made some tests be removed.

This PR addresses
https://github.com/llvm/llvm-project/pull/144465#issuecomment-3063422828.
Using `joinErrors` and `llvm:Error` instead of boolean values.

---------

Co-authored-by: joaosaffran <joao.saffran@microsoft.com>
Co-authored-by: Joao Saffran <{ID}+{username}@users.noreply.github.com>

This pr resolves some discrepancies in verification during `validate` in
`DXILRootSignature.cpp`.

Note: we don't add a backend test for version 1.0 flag values because it
treats the struct as though there is no flags value. However, this will
be used when we use the verifications in the frontend.

- Updates `verifyDescriptorFlag` to check for valid flags based on
version, as reflected [here](https://github.com/llvm/wg-hlsl/pull/297)
- Add test to demonstrate updated flag verifications
- Adds `verifyNumDescriptors` to the validation of `DescriptorRange`s
- Add a test to demonstrate `numDescriptors` verification
- Updates a number of tests that mistakenly had an invalid
`numDescriptors` specified

Resolves: https://github.com/llvm/llvm-project/issues/147107

Implements static samplers parsing from root signature metadata
representation. This is required to support Root Signatures in HLSL.
Closes: #[126641](https://github.com/llvm/llvm-project/issues/126641)

---------

Co-authored-by: joaosaffran <joao.saffran@microsoft.com>

In #144957 the backend was updated to expect a version in the metadata,
but since the frontend wasn't updated this breaks compilation. This is a
somewhat temporary fix to that until #144813 lands.

Implements descriptor table parsing from root signature metadata. This
is required to support root signatures in hlsl.
Closes: #[126640](https://github.com/llvm/llvm-project/issues/126640)

---------

Co-authored-by: joaosaffran <joao.saffran@microsoft.com>