build/lib/mangleTypeScript.ts/ClassData/_isNameTaken
class ClassData:	private _isNameTaken(name: string) {
		if (this.fields.has(name) && !ClassData._shouldMangle(this.fields.get(name)!.type)) {
			// public field
			return true;
		}
		if (this.replacements) {
			for (const shortName of this.replacements.values()) {
				if (shortName === name) {
					// replaced already (happens wih super types)
					return true;
				}
			}
		}
		if ((<any>this.node.getSourceFile()).identifiers instanceof Map) {
			// taken by any other usage
			if ((<any>this.node.getSourceFile()).identifiers.has(name)) {
				return true;
			}
		}
		return false;
	}