Fix for Exported typed variables in a tool script have wrong initial value if not initialized

[Hilderin]

This should fix #62363

The problem was caused by member_default_values_cache not initialized for tool scripts. When not a tool script, a PlaceHolder is created and _update_exports was called. But _update_exports was not called on the creation of GDScriptInstance. Later when the scene or the script is saved, _update_exports is called fixing the issue after the first save. So to fix the problem, I added a call to _update_exports when the GDScriptInstance is created.

[Hilderin]

Hi, can someone help me with the error from the CI pipeline for MacOS please?
I really have no clue what can be the problem and I don't have acces to a Mac, the Unit Tests pass on the other platforms but on MacOS, the build fail with this error:

TEST SUITE: [Modules][GDScript]
TEST CASE:  Script compilation and runtime

./modules/gdscript/tests/gdscript_test_runner_suite.h:43: FATAL ERROR: test case CRASHED: SIGSEGV - Segmentation violation signal

I found another PR #88452 talking about this error and wrapping code in #ifdef TOOLS_ENABLED but that code has this condition already.

Nevermind, after a good night of sleep, I figured it out, I just added if (Engine::get_singleton()->is_editor_hint()) before calling _update_exports.