Add runtime queries for tfvars (based on hcl)

[dxmh]

I noticed that the .tfvars files in my Terraform projects don't get syntax highlighting unless I manually run :set-language hcl.

The tfvars language is already configured to use the hcl grammar (since it was separated from hcl in #2244):

helix/languages.toml

Lines 1279 to 1288 in 0dbee95

	[[language]]
	name = "tfvars"
	scope = "source.tfvars"
	file-types = ["tfvars"]
	roots = []
	comment-token = "#"
	indent = { tab-width = 2, unit = " " }
	language-server = { command = "terraform-ls", args = ["serve"], language-id = "terraform-vars" }
	auto-format = true
	grammar = "hcl"

So this small PR adds the tfvars files into runtime/queries/, with each simply inheriting from hcl (as advised on Matrix by @archseer).

I've added files to inherit everything from hcl (folds, highlights, indents and injections), though I'm unsure if all are necessary, or if perhaps only highlights.scm should be added. Please let me know if anything needs to be changed.

Thanks!