refactor: swap SSBO bindings for TBOs

[NateSmyth]

Purpose

Remove SSBO bindings from the opengl backend in favor of TBOs
Expand hardware compatibility to any device meeting min OpenGL 4.3 specs

Implementation

1. Replace cell_text vertex SSBO with TBO

• Added buffer_texture option to Pipeline and TBO binding logic to RenderPass
• cell_text.v.glsl: SSBO bg_colors[] → usamplerBuffer + texelFetch.

2. Replace cell_bg fragment SSBO with TBO

• cell_bg.f.glsl: SSBO cells[] → usamplerBuffer + texelFetch
• Removed the SSBO binding loop from RenderPass
• Dropped unused .buffers from the bg_color step in generic renderer

Technically the change in generic.zig affects the metal backend but this was an unused binding.

3. Cleanup

• Removed GL_SHADER_STORAGE_BUFFER, InstanceBufferOptions
• Rewording comments
• Cleaned up my own dead code that I added...

Verify

• Build & ran on opengl (RTX 3070 + the original Radeon HD 7650A that was having issues), no issues in normal use
• Ditto on metal
• No regressions in tests

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Rework of #10952

• Keeps it contained to opengl
• Split off the CellText rework because its not directly related anymore. But compatible

The vertex attribute approach feels more surgical for my specific issue (vertex SSBO), but the TBO seems cleaner if you intend to remove the fragment SSBO, and keeps things contained within opengl code.

Either way fixes my issue (and fixes #8836)

[mitchellh]

This looks a lot better visually, I haven't run it yet. cc @qwerasd205 I'll look more deeply soon.