Custom core shader template

some of the vanilla core shaders are unintuitively named and needlessly repetitive, so i grouped many of the similar ones together and renamed them to more intuitively describe what they do

not all shaders are included, for example ones unobserved ingame such as new_entity or ones too niche to be useful, like water_mask

if there are any visual differences from vanilla lemme know

Changes from vanilla

• grouped all block / entity renderers in core/shared, tagged with #define s, and consolidated block and entity shader in include/render
• renamed many other unique renderers appropriately in core/render
• changed all cases of texelFetch(Sampler2, UV2 / 16., 0) to minecraft_sample_lightmap(Sampler2, UV2), this makes all lighting use the same function so changing lighting will be consistent.

for a comprehensive list of what each rendertype affects, see the community maintained shader wiki