Add reserved keywords

[sadikovi]

Requirements

• Filling out the template is required. Any pull request that does not include enough information to be reviewed in a timely manner may be closed at the maintainers' discretion.
• All new code requires tests to ensure against regressions

Description of the Change

This PR adds reserved keywords const and goto, so they are highlighted as standard keywords, e.g. try or catch, or instanceof. I assigned scope keyword.reserved.java for them, because I could not figure out what existing scope they should belong to, since they are not used:).

Looks like this now:

Alternate Designs

None were considered, because it is fairly simple change.

Benefits

Reserved keywords are now highlighted the same way as standard keywords.

Possible Drawbacks

None.

Applicable Issues

#136

[sadikovi]

@50Wliu Could you review this PR? Let me know if it should be added like this or we should add those keywords into one of the existing scopes. Thanks!

[winstliu]

Awesome. I love the addition of reserved, so that themes can style that how they wish.

[sadikovi]

Thanks @50Wliu! Will merge.