coreinit: Added support for 'wb' modifier flag in FSOpenFile()/SAVEOpenFile()

AX: Rewrote a majority of AX API and internal mixing code, aiming for almost a 1:1 reimplementation where possible
AX: Adjusted memory layout of some internal sample data buffers (some games calculate addresses on their own instead of relying on the values provided by the API)

SWKBD: Fixed a bug that caused the software keyboard overlay to not display on AMD GPUs

GX2: Added support for D24_S8_FLOAT depth buffer format
GX2: Shaders will now correctly use shadow samplers instead of imitating them by manually comparing shadow depth in shader logic
GX2: Added support for dynamically detecting and adjusting the number of mip levels of a texture during usage (information about the mip level count isn't always available at texture creation)
GX2: Better support for rendering to individual mip levels of a texture
GX2: Added support for binding the same texture multiple times with different mip or slice views during a drawcall
GX2: Fixed order of elements returned by FETCH4 shader instruction
GX2: Fixed a bug in polygon offset slope scale calculation
GX2: Handle texture LOD parameter correctly in vertex shader