CommonHost: Purge and move functions to appropriate locations

[stenzek]

Description of Changes

• Support building without -fno-operator-names
• Set UTF-8 source file format globally.
• Set permissive/compliance mode globally.
• Get rid of include of base 3rdparty directory, be explicit.
• Get rid of duplicated properties.
• Get rid of leftover plugin property files.
• Move everything from CommonHost to a better home.

Rationale behind Changes

Consistency across build systems, less mess. Less code.

Suggested Testing Steps

Make sure both MSVC and Clang builds work. Make sure performance hasn't changed since master.

Make sure discord presence, achievements pop up when starting a game, and play time tracking still works.