Fixing several embarrassing bugs.

WebGPU and REGL projects now flipY again, and they properly flip the symbolY glyph coordinate in the rain pass's fragment shader.
Switching on some older code that was disabled for FF Nightly support— it makes more sense to wait for that support as implementations finalize.
Added mipmap to images loaded into REGL project.

shaders/glsl/rainPass.frag.glsl

@@ -102,13 +102,13 @@ vec3 getBrightness(vec4 raindrop, vec4 effect, float quadDepth, vec2 uv) {
 vec2 getSymbolUV(float index) {
 	float symbolX = modI(index, glyphTextureGridSize.x);
 	float symbolY = (index - symbolX) / glyphTextureGridSize.x;
+	symbolY = glyphTextureGridSize.y - symbolY - 1.;
 	return vec2(symbolX, symbolY);
 }
 
 vec2 getSymbol(vec2 uv, float index) {
 	// resolve UV to cropped position of glyph in MSDF texture
 	uv = fract(uv * vec2(numColumns, numRows));
-	uv.y = 1.0 - uv.y; // y-flip
 	uv -= 0.5;
 	uv *= clamp(1. - glyphEdgeCrop, 0., 1.);
 	uv += 0.5;