Fix: TilingSprite gaps when mipmapping enabled

[ShukantPal]

Fixes #7625

Description of change

I added a comment in the issue describing the underlying problem. In this fix, I create two versions of the tiling sprite shader (leaving the "simple" variant alone):

• WebGL 1: GL_EXT_shader_texture_lod is used, when available, to sample the LOD 0 when texel is clamped to a different values (i.e. at the boundary of the texture, outside of the clamping region)
• WebGL 2: texture2DLodEXT is not available in WebGL 2. Instead, I use texture with a very negative LOD-bias when sampling at the boundary of the tiled texture.

NOTE: The GL_EXT_shader_texture_lod extension is not available on macOS Safari (WebGL 1). You can't test this fix on that! Enabling it in experimental features won't work for replit.com too.

Please see this reproduction and test whether the issue remains.

[eXponenta]

Android 11, Webgl2 (Adreno 330), DPI 2.5

[Bouh]

The gaps are still visible to me on Android 9 with Webgl2 on the mobile version of the website, but not on the desktop mode of the website

Gaps are gone on the PC 👍

[ShukantPal]

@eXponenta It may be because I hardcoded the DPI to 2 in the reproduction, and your device's DPI is 2.5

[bigtimebuddy]

Thanks @ShukantPal