[Reflection] Prevent symbolic reference mangling induced crash

[kastiglione]

Based on lldb crash logs, TypeRefBuilder is crashing on instances of symbolic references in mangled names.

The crash happens when a symbolic reference is attempted to be mangled (via mangleNode()), which leads to a call to unreachable which aborts. For library usage, such as from lldb, these cases need to be handled without an abort.

The improvements to gracefully handle symbolic references are:

1. Change the return type of normalizeReflectionName from std::string to llvm::Optional<std::string>
2. Thread through a bool flag named useOpaqueTypeSymbolicReferences

Both of these start in normalizeReflectionName.

First, the call to demangleTypeRef() now sets useOpaqueTypeSymbolicReferences to false. Without this, demangleTypeRef() can return a node of kind OpaqueTypeDescriptorSymbolicReference, which is guaranteed to fail in this code path when in subsequent call to mangleNode().

Second, if the result of demangleTypeRef() is one of the symbolic reference kinds, then the function exits early with a value of None. Callers of normalizeReflectionName() are now forced to handle such cases, where the mangled name could not be normalized.

In TypeRefBuilder::getFieldTypeInfo(), if normalizeReflectionName() fails, then the corresponding field is not supported, or in other words, dropped.

rdar://77613304

(cherry picked from #37514)

[kastiglione]

See #37514 for original context.

[kastiglione]

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