orccodemem: Add support for Universal Windows Platform apps

orccodemem: Add support for Universal Windows Platform apps

VirtualAlloc is VirtualAllocFromApp when targeting UWP, and you can
only allocate executable pages if you have the codeGeneration
capability set in the app manifest. Check for that capability in
_orc_compiler_init() and switch to backup code or emulation if it
isn't available instead of crashing when VirtualAllocFromApp
returns NULL.

Also you cannot allocate pages that are both READWRITE and EXECUTE, so
we allocate as read-write first, then set the memory as execute-only
after the code has been compiled and copied over.

Part-of: <https://gitlab.freedesktop.org/gstreamer/orc/-/merge_requests/42>