Defined WINDOWEVENT_MINIMIZED (so you don't have to check for '7')

[MyreMylar]

closes #1749 by finishing off the last remaining bit of work there resulting from unit testing display.iconify().

Previously you had to check for the number '7' to conclusively identify the event generated when a window was iconified in pygame 2/SDL 2. Now it has its correct SDL 2 name.

[MightyJosip]

Looks like we need to increase delta once again:

======================================================================
FAIL: test_delay (pygame.tests.time_test.TimeModuleTest)
Tests time.delay() function.
----------------------------------------------------------------------
Traceback (most recent call last):
  File "C:\Python38\lib\site-packages\pygame\tests\time_test.py", line 214, in test_delay
    self._wait_delay_check(pygame.time.delay, millis, iterations, delta)
  File "C:\Python38\lib\site-packages\pygame\tests\time_test.py", line 309, in _wait_delay_check
    self.assertAlmostEqual(wait_time, millis, delta=delta)
AssertionError: 111 != 50 within 50 delta (61 difference)
----------------------------------------------------------------------

[illume]

👍

[illume]

I wonder if this backwards compatibility should be captured in an issue?

I think it's easier for users to read the wording pygame 2, rather than SDL1 or SDL2. Since understanding SDL versions is maybe above the heads of most people.