Minimum contrast ratio isn't working for inverted text in DOM renderer

[Tyriar]

minimumContrastRatio = 4.5:

minimumContrastRatio = 9:

[meganrogge]

Dom:

Webgl:

[meganrogge]

bgL is calculated to be 0 for DOM

xterm.js/src/common/Color.ts

Lines 167 to 168 in de03391

	const bgL = rgb.relativeLuminance(bgRgba >> 8);
	const fgL = rgb.relativeLuminance(fgRgba >> 8);

vs webgl