GDScript: Fix setter being called in chains for shared types

When a type is shared (i.e. passed by reference) it doesn't need to be
called in a setter chain (e.g. `a.b.c = 0`) since it will be updated in
place.

This commit adds an instruction that jumps when the value is shared so
it can be used to skip those cases and avoid redundant calls of setters.
It also solves issues when assigning to sub-properties of read-only
properties.

modules/gdscript/gdscript_disassembler.cpp

@@ -838,6 +838,14 @@ void GDScriptFunction::disassemble(const Vector<String> &p_code_lines) const {
 
 				incr = 1;
 			} break;
+			case OPCODE_JUMP_IF_SHARED: {
+				text += "jump-if-shared ";
+				text += DADDR(1);
+				text += " to ";
+				text += itos(_code_ptr[ip + 2]);
+
+				incr = 3;
+			} break;
 			case OPCODE_RETURN: {
 				text += "return ";
 				text += DADDR(1);