support reading of pixels as float32

src/mol-geo/geometry/color-data.ts

src/mol-geo/geometry/marker-data.ts

src/mol-geo/geometry/overpaint-data.ts

src/mol-geo/geometry/size-data.ts

src/mol-geo/geometry/text/font-atlas.ts

src/mol-geo/geometry/text/text.ts

src/mol-geo/geometry/transparency-data.ts

src/mol-gl/renderable/util.ts

src/mol-gl/webgl/compat.ts

src/mol-gl/webgl/context.ts

src/mol-gl/webgl/texture.ts