**Description:**
Adds `IsMemberDataPointerType()` to CompilerType / TypeSystem /
TypeSystemClang, mirroring the existing `IsMemberFunctionPointerType()`.
LLDB already has `IsMemberFunctionPointerType()` to identify member
function pointers but no counterpart for member data pointers. The only
way to check for member data pointers was the indirect `GetTypeClass()
== eTypeClassMemberPointer && !IsMemberFunctionPointerType()`, which is
awkward.
This pr is split out from a larger [fix,
186629](https://github.com/llvm/llvm-project/pull/186629) for LLDB
mishandling non-type template parameters (NTTPs) of pointer-to-member
types, where cleanly distinguishing member data pointers from member
function pointers is needed. The new API delegates to clang's
`QualType::isMemberDataPointerType()` via the same I`sTypeImpl` pattern
used by `IsMemberFunctionPointerType`.
**Test Plan:**
Added `TestIsMemberDataPointerType` to `TestTypeSystemClang.cpp` that
verifies:
`int S::*` → `IsMemberDataPointerType() = true`,
`IsMemberFunctionPointerType() = false`
`void (S::*)()` → `IsMemberDataPointerType() = false`,
`IsMemberFunctionPointerType() = true`
`int * (regular pointer)` → both false
`int (non-pointer)`→ both false
e895a80b5d