Support dockerfiles (#1303)

* allow language.config (in languages.toml) to be passed in as a toml object

* Change config field for languages from json string to toml object

* remove indents on languages.toml config

* fix: remove patch version from serde_json import in helix-core

* Use same tree-sitter-zig as upstream/master

* fix(completion_popup): Fixes #1256

* Update helix-term/src/ui/completion.rs

* feat(languages): Add support for `Dockerfile`s

* docs(cargo-xtask-docgen):

* improvement(langs-dockerfile): Add `injection-regex` to `languages.toml` for
`Dockerfile`

* improvement(langs-dockerfile): Add injections.scm

* Update .gitmodules

Co-authored-by: Blaž Hrastnik <blaz@mxxn.io>

runtime/queries/dockerfile/highlights.scm

@@ -0,0 +1,51 @@
+[
+	"FROM"
+	"AS"
+	"RUN"
+	"CMD"
+	"LABEL"
+	"EXPOSE"
+	"ENV"
+	"ADD"
+	"COPY"
+	"ENTRYPOINT"
+	"VOLUME"
+	"USER"
+	"WORKDIR"
+	"ARG"
+	"ONBUILD"
+	"STOPSIGNAL"
+	"HEALTHCHECK"
+	"SHELL"
+	"MAINTAINER"
+	"CROSS_BUILD"
+] @keyword
+
+[
+	":"
+	"@"
+] @operator
+
+(comment) @comment
+
+
+(image_spec
+	(image_tag
+		":" @punctuation.special)
+	(image_digest
+		"@" @punctuation.special))
+
+(double_quoted_string) @string
+
+(expansion
+  [
+	"$"
+	"{"
+	"}"
+  ] @punctuation.special
+) @none
+
+((variable) @constant
+ (#match? @constant "^[A-Z][A-Z_0-9]*$"))
+
+