[AsmParser] Support non-consecutive global value numbers (#80013)

https://github.com/llvm/llvm-project/pull/78171 added support for
non-consecutive local value numbers. This extends the support for global
value numbers (for globals and functions).

This means that it is now possible to delete an unnamed global
definition/declaration without breaking the IR.

This is a lot less common than unnamed local values, but it seems like
something we should support for consistency. (Unnamed globals are used a
lot in Rust though.)