Treesitter parser (#2902)

A push towards better editor support.
See utils/treesitter/README.md

---------

Co-authored-by: josh11b <josh11b@users.noreply.github.com>

utils/treesitter/queries/highlights.scm

@@ -0,0 +1,132 @@
+; Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+; Exceptions. See /LICENSE for license information.
+; SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+; This maps syntax node patterns to highlighting scopes.
+; The scopes are used themes and editors to select style for that node.
+
+(comment) @comment
+(builtin_type) @type.builtin
+(bool_literal) @constant.builtin
+(escape_sequence) @constant.character.escape
+(string_literal) @string
+(numeric_literal) @constant.builtin
+(numeric_type_literal) @type.builtin
+
+; function declaration or call expression => function
+(function_declaration (declared_name (ident) @function))
+(call_expression (ident) @function)
+
+; TODO: add more specific rules
+
+; upper case => type
+((ident) @type
+  (#match? @type "^[A-Z]"))
+
+; lower case => variable
+((ident) @variable
+  (#match? @variable "^[a-z_]"))
+
+[
+  "("
+  ")"
+  "{"
+  "}"
+  "["
+  "]"
+] @punctuation.bracket
+
+[
+  "."
+  ";"
+  ","
+  ":"
+  ":!"
+  "=>"
+] @punctuation.delimiter
+
+"->" @punctuation
+
+[
+  "+"
+  "-"
+  (binary_star)
+  "/"
+  "%"
+  "=="
+  "!="
+  "<"
+  "<="
+  ">"
+  ">="
+  "not"
+  "and"
+  "or"
+  "|"
+  "&"
+  "^"
+  ">>"
+  "<<"
+  "*" ; prefix star
+  (postfix_star)
+  "++"
+  "--"
+] @operator
+
+; keywords not used in grammar.js are commented out
+[
+  "abstract"
+  ; "adapt"
+  "addr"
+  "alias"
+  "and"
+  "api"
+  "as"
+  "auto"
+  "base"
+  "break"
+  "case"
+  "choice"
+  "class"
+  "constraint"
+  "continue"
+  "default"
+  "destructor"
+  "else"
+  "extend"
+  ; "final"
+  "fn"
+  "for"
+  "forall"
+  ; "friend"
+  "if"
+  "impl"
+  "impls"
+  "import"
+  "in"
+  "interface"
+  "let"
+  "library"
+  ; "like"
+  "match"
+  "namespace"
+  "not"
+  ; "observe"
+  "or"
+  ; "override"
+  "package"
+  ; "partial"
+  ; "private"
+  ; "protected"
+  "require"
+  "return"
+  "returned"
+  "Self"
+  "template"
+  "then"
+  "type"
+  "var"
+  "virtual"
+  "where"
+  "while"
+] @keyword