Support dark and light high contrast theme types

[daviddossett]

Adding the new light high contrast theme (#143398) uncovered challenges across the codebase when attempting to render unique styles or assets based on the theme settings. Here's a simple example where the letterpress SVG used in an empty editor view was hardcoded for the original dark HC theme.

Proposal

Currently we only expose a general high contrast theme type. A couple of things I think would be worth supporting:

• Split hc into something like hc-light and hc-dark
• Support workbench.preferredLightHighContrastColorTheme and workbench.preferredDarkHighContrastColorTheme if we're able to pick up the OS mode as an additional input like we do for regular dark/light themes.

Ideally the outcome here is that we can continue to use the theme type as an input in both logic (e.g. this.theme.type === ColorScheme.LIGHT_HIGH_CONTRAST and in stylesheets (e.g. .hc-light or .hc-black).

It would be great to get any additonal thoughts/opinions. cc @isidorn @aeschli @misolori

[miguelsolorio]

I think this makes sense and we'll likely start seeing requests for this (to create a new Light HC based off the new version) so 👍

[isidorn]

I agree with the proposal, it makes sense. I know @aeschli is buried in issues so maybe somebody else can drive this debt work? Martin do you have suggestions?

fyi @bpasero

[bpasero]

Splitting hc up into hc-light and hc-dark resonates with me.

[aeschli]

Yes, makes sense.

[aeschli]

I'm happy to do the workbench theme service changes if you look at the css fixes.
Currently all colors have default colors for light, dark and hc. That means we would need new defaults for hc-light as well.

So it's quite some work...

[daviddossett]

I'm happy to do the workbench theme service changes if you look at the css fixes. Currently all colors have default colors for light, dark and hc. That means we would need new defaults for hc-light as well.

That works for me! 👍