[debug-info] As an NFC commit, refactor EmitFuncArgumentDbgValue so that it...

[debug-info] As an NFC commit, refactor EmitFuncArgumentDbgValue so that it can be extended to support llvm.dbg.addr.

The reason why I am making this change is that before this commit,
EmitFuncArgumentDbgValue relied on a boolean flag IsDbgDeclare both to signal
that a DBG_VALUE should be made to be indirect /and/ that the original intrinsic
was a dbg.declare. This is no longer always true if we add support for handling
dbg.addr since we will have an indirect DBG_VALUE that is a different intrinsic
from dbg.declare.

With that in mind, in this NFC patch, we prepare for future fixes by introducing
a 3 case-enum argument to EmitFuncArgumentDbgValue that allows the caller to
explicitly specify how the argument's DBG_VALUE should be emitted. This then
allows us to turn the indirect checks into a != FuncArgumentDbgValueKind::Value
and prepare us for a future where we add support here for llvm.dbg.addr
directly.

rdar://83957028

Reviewed By: aprantl

Differential Revision: https://reviews.llvm.org/D122945