feat(event): return event dsc for later to remove

[XuNeo]

Description of the feature or fix

Now event dsc is stored in an array by pointer. The pointer is returned to user and can be deleted laster with it.

Notes

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[kisvegabor]

The failing test:

/home/runner/work/lvgl/lvgl/tests/src/test_cases/widgets/test_switch.c:71:test_switch_should_not_leak_memory_after_deletion:FAIL: Expected 33527492 to be less than or equal to 33527488

4 byte of memory leak can be due to memory fragmentation too. Especially as the issue is not reported by other tests.

I suggest using TEST_ASSERT_MEM_LEAK_LESS_THAN with 8 byte of threshold.

[kisvegabor]

Thanks!