Some cleanup

- Use whateverEmitter.event for the onWhatever methods.
- Add readonly to a bunch of things.
- Remove some redundancy in types.
- Move initializations out of the constructor and into the declarations
  where it was reasonable to do so.
- Disable a few no-any violations.

packages/ide/src/fill/os.ts

@@ -13,7 +13,7 @@ class OS {
 
 	public homedir(): string {
 		if (typeof this._homedir === "undefined") {
-			throw new Error("not initialized");
+			throw new Error("trying to access homedir before it has been set");
 		}
 
 		return this._homedir;
@@ -21,7 +21,7 @@ class OS {
 
 	public tmpdir(): string {
 		if (typeof this._tmpdir === "undefined") {
-			throw new Error("not initialized");
+			throw new Error("trying to access tmpdir before it has been set");
 		}
 
 		return this._tmpdir;