[clang][bytecode] SourceInfo::Source might be null (#115905)

This broke in 23fbaff9a3fd2b26418e0c2f10b701049399251f, but the old
.dyn_cast<> handled null.

[ByteCode] Migrate away from PointerUnion::{is,get,dyn_cast} (NFC) (#115809)

Note that PointerUnion::{is,get,dyn_cast} have been soft deprecated in
PointerUnion.h:

// FIXME: Replace the uses o

[ByteCode] Migrate away from PointerUnion::{is,get,dyn_cast} (NFC) (#115809)

Note that PointerUnion::{is,get,dyn_cast} have been soft deprecated in
PointerUnion.h:

// FIXME: Replace the uses of is(), get() and dyn_cast() with
// isa<T>, cast<T> and the llvm::dyn_cast<T>

show more ...

[clang] Rename all AST/Interp stuff to AST/ByteCode (#104552)

"Interp" clashes with the clang interpreter and people often confuse
this.