Use different colors for object keys and string-based values in JSON listings

[JKRhb]

This simple PR should resolve #4635 by adding an item for the scope meta.mapping.key.json string.quoted.double.json to the default raw theme, changing the default color that is used for the keys within JSON objects. This makes it possible to differentiate keys from string-based values more easily.

I am currently not sure whether the color I've chosen so far is the best, so I am open for feedback here :) The changes themselves are hopefully trivial enough to still become part of the upcoming release.

[JKRhb]

As mentioned in #4635 (comment), another option could be using green for the keys and light blue for the values, which can also be set quite easily in the custom theme:

If that (or a different color scheme) would be preferable, this could be updated quite quickly.

[laurmaedje]

The contrast of the light blue against the background is quite bad (3.16:1 against #fdfdfd background, you can check online), which makes this non-accessible (we recently changed it to be more accessible in #6754). Maybe we can use one of the existing colors instead? I'd imagine that some of them aren't used at all yet in JSON.

[JKRhb]

Thank you for the feedback, @laurmaedje! I've now changed the theme to keep #198810 as the color for the keys and use #4b69c6 (which was already used elsewhere) for string-based values, which I think looks quite well and also passes the accessibility test.

To keep the default green color for the keys in nested objects, I had to still explicitly define

meta.mapping.key.json string.quoted.double.json

since

meta.mapping.value.json string.quoted.double.json

overrides the key color starting on the second level for some reason if the key color is not explicitly defined:

I therefore expanded the test I added before to also cover that case, yielding the following result when including both the color definitions for keys and values:

[laurmaedje]

I think that's much better. On second thought, I like your idea of highlighting the keys instead of the values blue better since the values feel more normal (= normal green string) while the keys are a bit more special.

[JKRhb]

I think that's much better. On second thought, I like your idea of highlighting the keys instead of the values blue better since the values feel more normal (= normal green string) while the keys are a bit more special.

Thank you! I've changed the theme accordingly :) I've also noticed by the way that the blue keys also correspond with the default theme used for YAML. To ensure that both types of raw elements stay consistent in terms of their theme, I took the freedom of also adding an equivalent test case for YAML, which also illustrates the similarities.

[JKRhb]

(Rebased my branch against the latest state of main).

@laurmaedje Let me know if there are any more things that should be changed to make this PR mergeable :)

[laurmaedje]

Nothing to do, I was just busy. Thanks!