[RFC][flang] Replace special symbols in uniqued global names. (#104859)

This change addresses more "issues" as the one resolved in #71338.
Some targets (e.g. NVPTX) do not accept global names containing
`.`. In particular, the global variables created to represent
the runtime information of derived types use `.` in their names.
A derived type's descriptor object may be used in the device code,
e.g. to initialize a descriptor of a variable of this type.
Thus, the runtime type info objects may need to be compiled
for the device.

Moreover, at least the derived types' descriptor objects
may need to be registered (think of `omp declare target`)
for the host-device association so that the addendum pointer
can be properly mapped to the device for descriptors using
a derived type's descriptor as their addendum pointer.
The registration implies knowing the name of the global variable
in the device image so that proper host code can be created.
So it is better to name the globals the same way for the host
and the device.

CompilerGeneratedNamesConversion pass renames all uniqued globals
such that the special symbols (currently `.`) are replaced
with `X`. The pass is supposed to be run for the host and the device.

An option is added to FIR-to-LLVM conversion pass to indicate
whether the new pass has been run before or not. This setting
affects how the codegen computes the names of the derived types'
descriptors for FIR derived types.

fir::NameUniquer now allows `X` to be part of a name, because
the name deconstruction may be applied to the mangled names
after CompilerGeneratedNamesConversion pass.