Add support for semantic tokens

[anthony-c-martin]

Would it be possible to add support for theming of semantic tokens to this theme? VSCode has a new mechanism for providing highlighting, and by default it is disabled for existing themes.

A number of extensions use it for enhanced colorization (I believe TypeScript, for example), but also fall back to using TextMate grammars for theming if support is not enabled. So generally many users may not notice that they don't have the enhanced highlighting available.

The extension I work on is new and does not have a fallback TextMate grammar, so if semantic token highlighting is disabled, there is 0 colorization available. You can download the extension here if you'd like to repro, and we have Azure/bicep#396 to track the issue generally on our side.

See https://code.visualstudio.com/api/language-extensions/semantic-highlight-guide#theming for some information about adding support for semantic highlighting.