GDScript LSP: Implement signatureHelp

Enable smart resolve default to true as it is required for script symbol lookup

modules/gdscript/language_server/gdscript_extend_parser.cpp

@@ -522,6 +522,51 @@ const lsp::DocumentSymbol *ExtendGDScriptParser::search_symbol_defined_at_line(i
 	return ret;
 }
 
+Error ExtendGDScriptParser::get_left_function_call(const lsp::Position &p_position, lsp::Position &r_func_pos, int &r_arg_index) const {
+
+	ERR_FAIL_INDEX_V(p_position.line, lines.size(), ERR_INVALID_PARAMETER);
+
+	int bracket_stack = 0;
+	int index = 0;
+
+	bool found = false;
+	for (int l = p_position.line; l >= 0; --l) {
+		String line = lines[l];
+		int c = line.length() - 1;
+		if (l == p_position.line) {
+			c = MIN(c, p_position.character - 1);
+		}
+
+		while (c >= 0) {
+			const CharType &charactor = line[c];
+			if (charactor == ')') {
+				++bracket_stack;
+			} else if (charactor == '(') {
+				--bracket_stack;
+				if (bracket_stack < 0) {
+					found = true;
+				}
+			}
+			if (bracket_stack <= 0 && charactor == ',') {
+				++index;
+			}
+			--c;
+			if (found) {
+				r_func_pos.character = c;
+				break;
+			}
+		}
+
+		if (found) {
+			r_func_pos.line = l;
+			r_arg_index = index;
+			return OK;
+		}
+	}
+
+	return ERR_METHOD_NOT_FOUND;
+}
+
 const lsp::DocumentSymbol *ExtendGDScriptParser::get_symbol_defined_at_line(int p_line) const {
 	if (p_line <= 0) {
 		return &class_symbol;