GDScript: Replace abstract keyword with @abstract annotation

Co-authored-by: Danil Alexeev <dalexeev12@yandex.ru>

modules/gdscript/tests/scripts/parser/errors/abstract_func_with_body.gd

@@ -1,8 +0,0 @@
-extends RefCounted
-
-abstract class A:
-	abstract func f():
-		pass
-
-func test():
-	pass

modules/gdscript/tests/scripts/parser/errors/abstract_func_with_body.out

@@ -1,2 +0,0 @@
-GDTEST_PARSER_ERROR
-Expected end of statement after abstract function declaration, found ":" instead.

modules/gdscript/tests/scripts/parser/errors/abstract_static_func.gd

@@ -1,8 +0,0 @@
-extends RefCounted
-
-abstract class A:
-	# Currently, an abstract function cannot be static.
-	abstract static func f()
-
-func test():
-	pass

modules/gdscript/tests/scripts/parser/errors/abstract_static_func.out

@@ -1,2 +0,0 @@
-GDTEST_PARSER_ERROR
-Expected "class" or "func" after "abstract".

modules/gdscript/tests/scripts/parser/errors/brace_syntax.out

@@ -1,2 +1,2 @@
 GDTEST_PARSER_ERROR
-Expected ":" after function declaration.
+Expected end of statement after bodyless function declaration, found "{" instead.

modules/gdscript/tests/scripts/parser/errors/duplicate_abstract_class.gd

@@ -1,7 +0,0 @@
-extends RefCounted
-
-abstract abstract class A:
-	pass
-
-func test():
-	pass

modules/gdscript/tests/scripts/parser/errors/duplicate_abstract_class.out

@@ -1,2 +0,0 @@
-GDTEST_PARSER_ERROR
-Expected "class_name", "extends", "class", or "func" after "abstract".

modules/gdscript/tests/scripts/parser/errors/duplicate_abstract_func.gd

@@ -1,7 +0,0 @@
-extends RefCounted
-
-abstract class A:
-	abstract abstract func f()
-
-func test():
-	pass

modules/gdscript/tests/scripts/parser/errors/duplicate_abstract_func.out

@@ -1,2 +0,0 @@
-GDTEST_PARSER_ERROR
-Expected "class" or "func" after "abstract".

modules/gdscript/tests/scripts/parser/errors/lambda_without_colon.gd

@@ -0,0 +1,3 @@
+#           No colon --v
+var f = func () -> void
+	pass

modules/gdscript/tests/scripts/parser/errors/lambda_without_colon.out

@@ -0,0 +1,2 @@
+GDTEST_PARSER_ERROR
+Expected ":" after lambda declaration.

modules/gdscript/tests/scripts/parser/errors/static_abstract_func.gd

@@ -1,8 +0,0 @@
-extends RefCounted
-
-abstract class A:
-	# Currently, an abstract function cannot be static.
-	static abstract func f()
-
-func test():
-	pass

modules/gdscript/tests/scripts/parser/errors/static_abstract_func.out

@@ -1,2 +0,0 @@
-GDTEST_PARSER_ERROR
-Expected "func" or "var" after "static".