file(GET_RUNTIME_DEPENDENCIES): Preserve casing for Windows PE binaries

For Windows PE files the `file(GET_RUNTIME_DEPENDENCIES)` command
converts the name of all  DLLs found during binary scanning to
lowercase in order to simplify the syntax requirements of its regex
filters; however, this has the side-effect of causing all DLL paths
returned via RESOLVED_DEPENDENCIES_VAR to be in lowercase, regardless
of their actual casing.

Instead, respect the original casing as closely as possible when
returning resolved dependencies after all filters have been
passed:

When evaluating a Windows PE format binary on a non-Windows host
the casing of dependencies recorded within the binary are
used. When the host is running Windows, the actual casing of the
dependencies on-disk are used instead.

Fixes: #23091