Add Discord Rich Presence support

Everywhere else throughout the codebase we use "Wiimote" when referring
to the Wii Remote as a shorthand. This makes the casing consistent.

BTEmu: Make m_WiiMotes private

This makes it much more straightforward to access WiimoteDevice
instances and also keeps the implementation details of accessing those
instances in one spot.

Given as all external accesses to the WiimoteDevice instances go through
this function, we can make the other two private.

I have no idea if this works or not. Hopefully the build bot will tell me.

Allows us to get rid of a silly pointer cast and deduplicate some code
from the front-end when it comes to reading the value.

Makes the enum values strongly-typed and prevents the identifiers from
polluting the PowerPC namespace. This also cleans up the parameters of
some functions where we were accepting an ambiguous int type and
expecting the correct values to be passed in.

Now those parameters accept a PowerPC::CPUCore type only, making it
immediately obvious which values should be passed in. It also turns out
we were storing these core types into other structures as plain ints,
which have also been corrected.

As this type is used directly with the configuration code, we need to
provide our own overloaded insertion (<<) and extraction (>>) operators
in order to make it compatible with it. These are fairly trivial to
implement, so there's no issue here.

A minor adjustment to TryParse() was required, as our generic function
was doing the following:

N tmp = 0;

which is problematic, as custom types may not be able to have that
assignment performed (e.g. strongly-typed enums), so we change this to:

N tmp;

which is sufficient, as the value is attempted to be initialized
immediately under that statement.

Rather than introduce this handling in every system instruction that modifies
the FPSCR directly, we can instead just handle it within the data structure
instead, which avoids duplicating mask handling across instructions.

This also allows handling proper masking from the debugger register
windows themselves without duplicating masking behavior there either.