Provide token modifiers for traversals (references)

[radeksimko]

This is in follow-up to #833

Background

In the above PR we introduce custom semantic token types and modifiers, to enable themes to address configuration parts more accurately and using more familiar names.

Modifiers per traversal segment

There are some ideas shared by a theme creator who mentioned they'd want to highlight each segment separately, i.e. for data.aws_availability_zones.available.names there would be 4 different modifiers.

• Different textmate scopes for members vscode-terraform#574 (comment)
• Different textmate scopes for members vscode-terraform#574 (comment)

And there are some limitations discovered in hashicorp/vscode-terraform#574 (comment). That's not to say these are unsolvable but may present some challenges and additional overhead in implementation.

Modifiers for whole traversal

We could also provide modifier for the whole traversal, e.g. reuse terraform-data for data.aws_availability_zones.available.names and generally any references to data blocks.

Proposal

TODO