feat(highlight): add TOML syntax highlighting

Use tree-sitter-toml-ng v0.7.0 from tree-sitter-grammars, which is
compatible with tree-sitter 0.26 (unlike the older tree-sitter-toml).

- Add tree-sitter-toml-ng dependency
- Add Toml variant to Language enum
- Add TOML_CONFIG with crate's HIGHLIGHTS_QUERY

Cargo.lock

@@ -1535,6 +1535,7 @@ dependencies = [
  "tree-sitter-nix",
  "tree-sitter-python",
  "tree-sitter-rust",
+ "tree-sitter-toml-ng",
  "tree-sitter-typescript",
  "tree-sitter-yaml",
  "walkdir",
@@ -1850,6 +1851,16 @@ dependencies = [
  "tree-sitter-language",
 ]
 
+[[package]]
+name = "tree-sitter-toml-ng"
+version = "0.7.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e9adc2c898ae49730e857d75be403da3f92bb81d8e37a2f918a08dd10de5ebb1"
+dependencies = [
+ "cc",
+ "tree-sitter-language",
+]
+
 [[package]]
 name = "tree-sitter-typescript"
 version = "0.23.2"