Feature request: Implement syntax highlighting support for Dart/Flutter

Feature request

Add syntax highlighting support for the Dart (and Flutter) programming language.
Official Dart VS Code extension syntax files https://github.com/Dart-Code/Dart-Code/tree/master/syntaxes
Monaco language configuration for Dart

const dartConfiguration = {
    comments: {
		lineComment: "//",
		blockComment: [ "/*", "*/" ]
	},
	brackets: [
		["{", "}"],
		["[", "]"],
		["(", ")"]
	],
	autoClosingPairs: [
		{ open: "{", close: "}" },
		{ open: "[", close: "]" },
		{ open: "(", close: ")" },
		{ open: "'", close: "'", notIn: ["string", "comment"] },
		{ open: "\"", close: "\"", notIn: ["string"] },
		{ open: "`", close: "`", notIn: ["string", "comment"] },
		{ open: "/**", close: " */", notIn: ["string"] }
	],
	surroundingPairs: [
		["{", "}"],
		["[", "]"],
		["(", ")"],
		["<", ">"],
		["'", "'"],
		["\"", "\""],
		["`", "`"]
	]
};

Help Wanted

Start by reviewing the official Dart VS Code syntax files linked in the issue and the provided Monaco language configuration. Compare those definitions with Monaco's existing language support, then verify that Dart and Flutter code receives syntax highlighting and the listed comments, brackets, and auto-closing behavior.