…dator (microsoft#7409)

This change removes the code meant to pass through to DXIL.dll when
creating a CLSID_DxcValidator object with DxcCreateInstance.

Since the internal validator is now the default, and it will sign
shaders, there is no reason to pass through to DXIL.dll when using
DxcCreateInstance on DxCompiler.dll.

Testing will come with planned work to include the ability to globally
override the default validator to external.

…versoin (microsoft#7408)

Internal testing using older validators reveals some failures on tests
that were intended to be run on newer validators. This PR changes the
tests to require a minimum validation version to run.

Validate:
 HitObject_FromRayQuery
 HitObject_FromRayQueryWithAttrs

Rules:
 No `undef` inputs

SER implementation tracker: microsoft#7214

Validate:
 HitObject_Invoke
 HitObject_TraceRay

Rules:
 No undef params
 Resource handle must be AS

SER implementation tracker: microsoft#7214

We will get a crash when use spirv intrinsic to create a constant value.
```fundamental
fatal error: generated SPIR-V is invalid: Constant cannot appear in a function declaration
  %spirvIntrinsicType_42 = OpConstant %spirvIntrinsicType 42
```

Show 'REORDER_SCOPE' memory flag rejected pre DXIL 1.9. REORDER_SCOPE
validation logic already implemented in microsoft#7263

Move REORDER_SCOPE validation tests to `LitDXILValidation/` and adapt
RUN lines as we are touching this (microsoft#7359).

SER implementation tracker: microsoft#7214

This PR removes a dead fallthrough statement after a switch-statement's
case that is terminated by a break;
This needs to be removed, because the way linux builds dxc in our
internal infrastructure, it errors when a dead fallthrough statement is
detected.
For context, here is the relevant error:

```
ScalarReplAggregatesHLSL.cpp:2822:9: error: fallthrough annotation in unreachable code [-Werror,-Wimplicit-fallthrough]
        LLVM_FALLTHROUGH;
        ^
... DXC/include/llvm/Support/Compiler.h:224:26: note: expanded from macro 'LLVM_FALLTHROUGH'
#define LLVM_FALLTHROUGH [[fallthrough]]
                         ^
1 error generated.
```

This updates the clang-format-checker action workflow to pull the format
checker and tools from `main` instead of from the PR.

Note: This PR basically can't be tested pre-merge since the pre-merge
check will use the version of the action in `main`.

Several intrinsics that were enabled for native vectors late got their
testing removed as it expected scalarized forms. This adds tests for
pow, modf, and abs in their native vector intrinsic forms. It removes
native vector intrinsics for derivative operations as they require more
scalarization removal due to their convergent markers and restores the
scalarized testing for them. The 1024 size was removed from
longvec-intrinsics as the verbose way that constant vectors are
represented in the disassembly made the test take significantly longer.

This PR removes the select-validator option. It is being deprecated, and
it wasn't ever officially documented.
Fixes microsoft#7419