wheel event handler not stopping default browser scroll action

[jerch]

Coming from #3514.

We currently register 2 default wheel event handlers, and a 3rd one if the app asked for wheel mouse reports:

• Terminal.ts:797
  This one is faulty. It handles the case to scroll within alternate buffer apps by sending cursor offsets. It is set to passive: true, thus will not stop the browser from doing its div/window scrolling on wheel. Should be passive: false and stop the event.
• Terminal.ts:823
  Not quite sure, why we have this one as a separate handler, imho it should be merged with the first one to remove some event listener stress.
• Terminal.ts:700
  This one creates the mouse wheel reports and stops the event, effectively skipping the other ones.

Fix:

• merge Terminal.ts:797 and Terminal.ts:823 into one handler
• properly stop event, if it already got handled within the terminal viewport
• set passive: false