Remove left margin when scrolling

[makew0rld]

Due to the change in 90654cd (as a part of #107, to fix #26) the left margin on pages was made into a UI element. That means that when scrolling to the right, for long pre-formatted lines, they appear to "disappear" under the left margin. This is an undesirable effect.

One solution would be to change the size of the margin when scrolling, and eventually remove it once its width becomes <= 0. Another possible solution would be to find a way to keep the left margin "underneath" the text.

[makew0rld]

cc @objectliteral for originally bringing this up

[makew0rld]

This can probably be done by using SetInputCapture on the TextView, and changing the margin size if scroll keys are being used. That would be left and right arrow, as well as h and l.

[makew0rld]

This is almost done, and the work is on the issue-197 branch. cview will need to be modified to continue. I will make the modifications and switch to using my fork, and then make a PR for it.

[makew0rld]

Branch has been merged, this issue is fixed! I opened this upstream PR.

[makew0rld]

This is still broken. If you go to gemini://makeworld.space/test/wrapping-test.gmi and scroll to the bottom, then start scrolling to the right, it will jump back up to the longest line.