Remove config option for dart_highlight_types

[natebosch]

See discussion in #94 (comment)

I think we should consider removing this option in the interest of having a smaller config surface area. We default to enabled, and users have another option to disable other than setting the variable. They could instead to hi link dartTypeName Normal.

cc @cbracken @sigmundch - do you have any thoughts?

[sigmundch]

No strong preference here. I would like us to document it clearly though. The :help doesn't mention dart_highlight_types, but does include dart_coretypes_highlight.

Speaking of which, I'd also remove the flag for the coretypes.

I think the group still has value, since dartTypeName can match a lot more, but the list of core-types is a well defined list and less likely to cause trouble. Do you agree?

[natebosch]

+1 on improving the documentation for this - I can add an example in the docs about how to clear out each of these highlight groups.

+1 on removing the flag for coretypes at the same time, with the same reasoning.

+1 on keeping the core types, and the user types based on capitalization, as separate highlight groups so that users have the option of flipping them individually.

What I might do is rename some of the groups, link them all into dartType, then link that to Type. This would maintain the ability to pick and choose which to disable, and make it easy to turn off all type highlighting with hi link dartType Normal.

Once we get a few of the other PRs settled I'll open up a new one with a proposal for this.