Cache pixiesmall.j2c in a pointer to prevent deep recursive directory search every time a particle with default texture is created or updated

Clear Vector4a using _mm_setzero_ps(); as that optimizes out to a nearly free instruction on modern processors vs fetching a zero array from memory

Replace dynamic_cast with static_cast as these never actually need or seem to be checked, except the one.

Fix constant reallocation of texture fetch command queue because...who..uses a vector..for a fifo...

May contain Kitty codez

SL-11589

Approved-by: Dave Houlton <euclid@lindenlab.com>

SL-12574 tweak brightness

Approved-by: Dave Houlton <euclid@lindenlab.com>

This reverts commit d67f05f9.