[WIP] GS/HW: Initial work implementing RT in RT support

[refractionpcsx2]

NOTE THIS IS HEAVY WIP, THIS IS NOT READY FOR CONSUMPTION, BUILDS ARE ONLY HERE FOR TESTING PURPOSES

Description of Changes

Adds support for render target inside render target draws and shuffles

Rationale behind Changes

We didn't support this and a bunch of games do it.

Suggested Testing Steps

Test games which had "top left corner" bugs or weird half screen problems.

Known to fix: Hitman Blood Money Swat Global Strike Team split screen Jak X split screen Suikoden 3 black and white scene with half screen problem Big Mutha Truckers

Improves but doesn't currently fix: Hitman Contracts (still slightly broken) Stolen (mostly, we have depth precision issues breaking the last bit) Pachipara Raw Danger Steambot Chronicles

Note: This is gated behind Tex in RT and will break some games if left on, be it on your own head!