Color contrast cache will have conflicting keys for different color modes

[Tyriar]

The cache key is based on the fg and bg color raw value:

xterm.js/src/browser/renderer/dom/DomRendererRowFactory.ts

Line 170 in 8b5c48f

let adjustedColor = this._colors.contrastCache.getColor(this._workCell.bg, this._workCell.fg);

This will overlap for different color modes.

[jerch]

All JS engines I can test have show 9007199254740991 as Number.MAX_SAFE_INTEGER. Not sure if thats the case only for 64bit (cannot test 32bit). There are 52 safe bits to be used (guess its double based internally), thus you could simply join BG and FG into one number as key with all rgb channels (= 48 bit).

[Tyriar]

@jerch it's probably easier to leave as is with the 2 separate keys to reduce fiddling with colors in this hot path.

Looking at this again, it's actually not a problem. I thought fg and bg just includes the number from getFgColor/getBgColor but it's not. #2602 just happens to work by accident because I only read 0xFFFFFF and the color mode is stored beyond that in 0x3000000