Fix extra underscore getting added to properties that start with double underscores

Internally, typescript seems to add an extra underscore to identifiers
that start with two underscores and based on
https://github.com/microsoft/TypeScript-wiki/blob/master/API-Breaking-Changes.md#typescript-30
unescapeLeadingUnderscores is the type-safe way of inverting this:

"...the typesafe escapeLeadingUnderscores and unescapeLeadingUnderscores
should be used if the types indicate they are required (as they are used
to convert to or from branded __String and string types)."

Author: Pedram Razavi

src/transformer.ts

@@ -253,7 +253,7 @@ function createTransformerFactory(program: ts.Program, options?: Partial<RenameO
 				throw new Error(`Cannot get symbol for node "${oldProperty.getText()}"`);
 			}
 
-			const oldPropertyName = symbol.escapedName as string;
+			const oldPropertyName = ts.unescapeLeadingUnderscores(symbol.escapedName);
 
 			return createNewNode(oldPropertyName, type, createNode);
 		}

tests/test-cases/ts-escaped-identifiers/input.ts

@@ -0,0 +1,6 @@
+class DoubleUnderscoreProperty {
+	public __foo: string = "bar";
+}
+
+const testObject = new DoubleUnderscoreProperty();
+export const foo = testObject.__foo + "baz";

tests/test-cases/ts-escaped-identifiers/output.js

@@ -0,0 +1,11 @@
+"use strict";
+Object.defineProperty(exports, "__esModule", { value: true });
+exports.foo = void 0;
+var DoubleUnderscoreProperty = /** @class */ (function () {
+    function DoubleUnderscoreProperty() {
+        this._internal___foo = "bar";
+    }
+    return DoubleUnderscoreProperty;
+}());
+var testObject = new DoubleUnderscoreProperty();
+exports.foo = testObject._internal___foo + "baz";