Add dotenv support (#273074)

* Add dotenv support

This adds basic language support for the dotenv language. This includes
syntax highlighting and a language configuration file.

The dotenv language is applied to files with the `.env` extension, files
named `.env`, `.flaskenv`, or `user-dirs.dirs`, and file names starting
with `.env.`.

The grammar is downloaded from https://github.com/dotenv-org/dotenv-vscode.

Closes #267333

* Add tests

* Remove ini and shellscript language conflicting with dotenv

---------

Co-authored-by: Alex Ross <38270282+alexr00@users.noreply.github.com>

extensions/dotenv/language-configuration.json

@@ -0,0 +1,24 @@
+{
+	"comments": {
+		"lineComment": "#"
+	},
+	"brackets": [
+		["{", "}"],
+		["[", "]"],
+		["(", ")"]
+	],
+	"autoClosingPairs": [
+		["{", "}"],
+		["[", "]"],
+		["(", ")"],
+		["\"", "\""],
+		["'", "'"]
+	],
+	"surroundingPairs": [
+		["{", "}"],
+		["[", "]"],
+		["(", ")"],
+		["\"", "\""],
+		["'", "'"]
+	]
+}