fix(terminal): correctly forward mouse events

[zeertzjq]

Fix #16371.

[zeertzjq]

Tests fail if I revert the change:

[  FAILED  ] 2 tests, listed below:
[  FAILED  ] test/functional/terminal/mouse_spec.lua @ 63: :terminal mouse when the terminal has focus with mouse events enabled by the program will forward mouse press, drag and release to the program
test/functional/terminal/mouse_spec.lua:96: Row 6 did not match.
Expected:
  |line27                                            |
  |line28                                            |
  |line29                                            |
  |line30                                            |
  |mouse enabled                                     |
  |*         #$#{1: }                                     |
  |{3:-- TERMINAL --}                                    |
Actual:
  |line27                                            |
  |line28                                            |
  |line29                                            |
  |line30                                            |
  |mouse enabled                                     |
  |*      @$#{1: }                                        |
  |{3:-- TERMINAL --}                                    |

To print the expect() call that would assert the current screen state, use
screen:snapshot_util(). In case of non-deterministic failures, use
screen:redraw_debug() to show all intermediate screen states.  

stack traceback:
	test/functional/ui/screen.lua:595: in function '_wait'
	test/functional/ui/screen.lua:362: in function 'expect'
	test/functional/terminal/mouse_spec.lua:96: in function <test/functional/terminal/mouse_spec.lua:63>

[  FAILED  ] test/functional/terminal/mouse_spec.lua @ 121: :terminal mouse when the terminal has focus with mouse events enabled by the program dragging and scrolling do not interfere with each other
test/functional/terminal/mouse_spec.lua:134: Row 6 did not match.
Expected:
  |line27                                            |
  |line28                                            |
  |line29                                            |
  |line30                                            |
  |mouse enabled                                     |
  |*   `"#{1: }                                           |
  |{3:-- TERMINAL --}                                    |
Actual:
  |line27                                            |
  |line28                                            |
  |line29                                            |
  |line30                                            |
  |mouse enabled                                     |
  |*      `"#{1: }                                        |
  |{3:-- TERMINAL --}                                    |

To print the expect() call that would assert the current screen state, use
screen:snapshot_util(). In case of non-deterministic failures, use
screen:redraw_debug() to show all intermediate screen states.  

stack traceback:
	test/functional/ui/screen.lua:595: in function '_wait'
	test/functional/ui/screen.lua:362: in function 'expect'
	test/functional/terminal/mouse_spec.lua:134: in function <test/functional/terminal/mouse_spec.lua:121>


 2 FAILED TESTS

[erw7]

I checked terminal.c of vim and found the same process, so I think this change is fine.

[bfredl]

@zeertzjq LGTM, rebase?

[zeertzjq]

Hmm, CI seems to be encountering some Internet problems.

[zeertzjq]

Oh, CI passed.

[Kavantix]

Would be nice to have a build with this fix 😇

[zeertzjq]

ping @bfredl

[bfredl]

Thanks!