[mono] Move basic w32file* and w32process* functions to eventpipe (#66731)

[mono] Move basic w32file* and w32process* functions to eventpipe (#66731)

They are not used by the rest of the runtime and we only need a bare minimum of w32process and w32file in eventpipe (e.g. no file share/access logic).

Fix ep-test build and warnings, it was missing linking against libz and monoapi.

Fix host vs. target confusion in ep-rt-mono.c

Move initialization of num_main_args after setting main_args in object.c so we can use it as a cheap guard value (not totally thread-safe but good enough for our purposes).

Co-authored-by: Johan Lorensson <lateralusx.github@gmail.com>