Fix global access of MonacoEnvironment (microsoft#248075)

Fix global access of MonacoEnvironment

There are 3 ways to declare global variables in TypeScript.

1. A global `declare let`.
2. A global `declare var`.
3. Augmenting the global `Window`.

There are 4 ways to access global variables in the browser.

1. Using a global identifier.
2. Using the `globalThis` object.
3. Using the `window` object.
4. Using the `self` object.

Not all 3 types of global declarations work for all methods to access a
global.

|              | `let` | `var` | `Window` |
| ------------ | ----- | ----- | -------- |
| global       |   ✓   |   ✓   |          |
| `globalThis` |       |   ✓   |          |
| `window`     |       |   ✓   |    ✓     |
| `self`       |       |   ✓   |    ✓     |

So the proper way to declare the global `MonacoEnvironment`, is:

```ts
declare global var MonacoEnvironment: Environment | undefined
```

https://www.typescriptlang.org/play/?#code/PQgEB4CcFMDNpgOwMbVAGwJYCMC8AiAEwHsBbfUYAPgFgAoew6ZdAQxlAHN1jtX1QAb3qhRGaABdQAGUkAuUAGcJkTIk4ixAN3agAauwXLV6+ptFqJCWK1SgA6mpIB3IebGjHiIyrUa6HgC+9MEMdGDcvPygtqiKivSyEvQGkPReZuHAoM5OxK6ckvS5iC4AdEnFec5lqVWl+WUZYWAlLkpFdG2NSaC4oADkA-XlqX2Dw13VTWrjQ5kRPHzoACoAFpiKXJ2Ry+ubFTtL-PuKtez0uycbZ830i1GrNx3JdFdPB73982-HH2djb6Td6nGaIOaTe7ZRTQdCwbavGFww6I2Gwc5pOhI9F3LIdOEvejYlEQolojGkrHkryU+jQAAeAAdiJApIJAkA

---------

Co-authored-by: Henning Dieterichs <hdieterichs@microsoft.com>

Author: remcohaszing

build/gulpfile.editor.js

@@ -116,12 +116,8 @@ function toExternalDTS(contents) {
 			lines[i] = line.replace('declare namespace monaco.', 'export namespace ');
 		}
 
-		if (line.indexOf('declare let MonacoEnvironment') === 0) {
-			lines[i] = `declare global {\n    let MonacoEnvironment: Environment | undefined;\n}`;
-		}
-
-		if (line.indexOf('\tMonacoEnvironment?') === 0) {
-			lines[i] = `    MonacoEnvironment?: Environment | undefined;`;
+		if (line.indexOf('declare var MonacoEnvironment') === 0) {
+			lines[i] = `declare global {\n    var MonacoEnvironment: Environment | undefined;\n}`;
 		}
 	}
 	return lines.join('\n').replace(/\n\n\n+/g, '\n\n');

build/monaco/monaco.d.ts.recipe

@@ -3,11 +3,8 @@
  *  Licensed under the MIT License. See License.txt in the project root for license information.
  *--------------------------------------------------------------------------------------------*/
 
-declare let MonacoEnvironment: monaco.Environment | undefined;
-
-interface Window {
-	MonacoEnvironment?: monaco.Environment | undefined;
-}
+// eslint-disable-next-line no-var
+declare var MonacoEnvironment: monaco.Environment | undefined;
 
 declare namespace monaco {
 

src/vs/monaco.d.ts

@@ -3,11 +3,8 @@
  *  Licensed under the MIT License. See License.txt in the project root for license information.
  *--------------------------------------------------------------------------------------------*/
 
-declare let MonacoEnvironment: monaco.Environment | undefined;
-
-interface Window {
-	MonacoEnvironment?: monaco.Environment | undefined;
-}
+// eslint-disable-next-line no-var
+declare var MonacoEnvironment: monaco.Environment | undefined;
 
 declare namespace monaco {