Reland "[lldb][DWARFASTParserClang] Fetch constant value from variable defintion if available" (#71800)

This patch relands https://github.com/llvm/llvm-project/pull/71004 which
was reverted because the clang change it depends on was reverted.

In addition to the original patch, this PR includes a change to
`SymbolFileDWARF::ParseVariableDIE` to support CU-level variable
definitions that don't have locations, but represent a constant value.
Previously, when debug-maps were available, we would assume that a
variable with "static lifetime" (which in this case means "has a linkage
name") has a valid address, which isn't the case for non-locationed
constants. We could omit this additional change if we stopped attaching
linkage names to global non-locationed constants.

Original commit message:
"""
https://github.com/llvm/llvm-project/pull/71780 proposes moving the
`DW_AT_const_value` on inline static members from the declaration DIE to
the definition DIE. This patch makes sure the LLDB's expression
evaluator can continue to support static initialisers even if the
declaration doesn't have a `DW_AT_const_value` anymore.

Previously the expression evaluator would find the constant for a
VarDecl from its declaration `DW_TAG_member` DIE. In cases where the
initialiser was specified out-of-class, LLDB could find it during symbol
resolution.

However, neither of those will work for constants, since we don't have a
constant attribute on the declaration anymore and we don't have
constants in the symbol table.
"""

Depends on:
* https://github.com/llvm/llvm-project/pull/71780

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