This patch updates the frontend to support version 1.2 of root
signatures, it adds parsing, metadata generation and a few tests.

---------

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

Remove:

* DescriptorType enum - this almost exactly shadowed the ResourceClass
enum
* ClauseType aliased ResourceClass

Although these were introduced to make the HLSL root signature handling
code a bit cleaner, they were ultimately causing confusion as they
appeared to be unique enums that needed to be converted between each
other.

Closes #153890

This patch refactors DXILABI to remove the dependency on scope printer. 
Closes: #153827

---------

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

As part of the Root Signature Spec, we need to validate if Root
Signatures are not defining overlapping ranges.
Closes: https://github.com/llvm/llvm-project/issues/126645

---------

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

During the split of the various `Frontend/HLSL` libraries, there was an
oversight to duplicate the `ResourceClassNames` definitions. This commit
simply consolidates the definitions into `DXContainer.h` as
`getResourceClasses`

Introduce the `enumToStringRef` enum into `ScopedPrinter.h` that
replicates `enumToString` behaviour, expect that instead of returning a
hex value string, it just returns an empty string. This allows us to
return a StringRef and easily check if an invalid enum was provided
based on the StringRef size

This then uses `enumToStringRef` to remove the redundant
`getResourceName` and `printEnum` functions.

Resolves: https://github.com/llvm/llvm-project/issues/151200.

This pr breaks-up `HLSLRootSignatureUtils` into separate orthogonal and
meaningful libraries. This prevents it ending up as a dumping grounds of
many different parts.

- Creates a library `RootSignatureMetadata` to contain helper functions
for interacting the root signatures in their metadata representation
- Create a library `RootSignatureValidations` to contain helper
functions that will validate various values of root signatures
- Move the serialization of root signature elements to
`HLSLRootSignature`

Resolves: https://github.com/llvm/llvm-project/issues/145946

`HLSLRootSignature.h` was originally created to hold the struct
definitions of an `llvm::hlsl::rootsig::RootElement` and some helper
functions for it.

However, there many users of the structs that don't require any of the
helper methods. This requires us to link the `FrontendHLSL` library,
where we otherwise wouldn't need to.

For instance:
- This [revert](https://github.com/llvm/llvm-project/pull/142005) was
required as it requires linking to the unrequired `FrontendHLSL` library
- As part of the change required here:
https://github.com/llvm/llvm-project/issues/126557. We will want to add
an `HLSLRootSignatureVersion` enum. Ideally this could live with the
root signature struct defs, but we don't want to link the helper objects
into `clang/Basic/TargetOptions.h`

This change allows the struct definitions to be kept in a single header
file and to then have the `FrontendHLSL` library only be linked when
required.

Implements metadata generation of a Root Signature from its in-memory
representation. It follows the same style as:
https://github.com/llvm/llvm-project/pull/139633.

This pr handles RootFlags, RootConstants and RootDescriptors.

The metadata follows the format described
[here](https://github.com/llvm/wg-hlsl/blob/main/proposals/0002-root-signature-in-clang.md#metadata-schema).

- Implement `BuildRoot[Flags|Constants|Descriptors]` into
`HLSLRootSignature.h`
- Add sample testcases demonstrating functionality

Note: there is no validation of metadata nodes as the
`llvm::hlsl::rootsig::RootElement` that generates it will have already
been validated.

First part of https://github.com/llvm/llvm-project/issues/126586.

The commit caused build failures,
[here](https://lab.llvm.org/buildbot/#/builders/10/builds/6308), due to
a missing linked llvm library (HLSLFrontend) into
`clang/unittests/Parse/CMakeLists.txt`.

While it seems like the fix is straightforwardly to just add this
library, I will revert now to build and verify locally it correctly
fixes it.

Reverts llvm/llvm-project#141130