[CIR] Add support for typeid l-value emission

[lanza]

Stack from ghstack (oldest at bottom):

• -> [CIR] Add support for typeid l-value emission #2000
• [CIR] Fix assertion failure in CIRGenRecordLayout for Empty Base Optimization #1999
• [CIR] Add support for ExtVector Bool Type #1998

Summary:
This patch implements support for emitting typeid expressions as
l-values in ClangIR, enabling code patterns such as:
const std::type_info& ti = typeid(MyClass);
auto& ref = typeid(int);
void foo(const std::type_info& ti) { foo(typeid(SomeType)); }

This is a common pattern in C++ code that uses RTTI for logging,
serialization, debugging, and type introspection.

Implementation:
The implementation follows the traditional LLVM CodeGen approach:

1. Added emitCXXTypeidExpr() in CIRGenExprCXX.cpp

   • Handles both type operands (typeid(Type)) and expression operands
     (typeid(expr))
   • Retrieves the RTTI descriptor via getAddrOfRTTIDescriptor()
   • Looks up the GlobalOp to determine the correct pointer type
   • Creates a GetGlobalOp to materialize the address at runtime
   • Polymorphic type vtable lookup is marked as NYI

2. Added emitCXXTypeidLValue() in CIRGenExpr.cpp

   • Calls emitCXXTypeidExpr() to get the RTTI descriptor pointer
   • Performs a bitcast from !u8i pointer to the proper type_info type
   • Creates an LValue with appropriate alignment for reference binding

3. Extended the emitLValue() switch statement to handle CXXTypeidExpr

What works:

• typeid with type operands: typeid(int), typeid(MyClass)
• typeid with non-polymorphic expression operands: typeid(obj)
• Reference binding: const std::type_info& ti = typeid(...)
• Function argument passing: foo(typeid(...))
• Built-in types, class types, and struct types

What doesn't work yet:

• typeid with polymorphic types requiring vtable lookup
  (e.g., typeid(*basePtr) where the dynamic type differs from static type)
  This is marked with llvm_unreachable() and will be implemented separately.

Test Plan:
Added comprehensive test coverage in clang/test/CIR/CodeGen/typeid-lvalue.cpp

• Non-polymorphic struct types
• Expression operands
• Built-in types (int, double)
• Function argument passing
• All tests pass

Regression testing:

• All 394 CIR CodeGen tests pass (379 passed, 14 unsupported, 1 expected fail)
• Code formatted with clang-format
• Code checked with clang-tidy (warnings consistent with existing codebase)

Differential Revision: N/A