Add support for modifier keys while scrolling in some terminals

[g-dg]

This PR adds support for the shift (horizontal scroll) and alt (fast scroll) key modifiers while scrolling. It also adds support for horizontal scroll wheels.

Unfortunately, it doesn't work in every terminal. Here are my testing results with some terminals:

Testing results with various terminals

Terminal	Horizontal scroll wheel	Shift + vertical scroll	Alt + vertical scroll	Alt + horizontal scroll wheel	Alt + shift + vertical scroll	Notes
Windows						(Windows 11)
Windows Terminal	❌	❌	✅	❌	❌	only sends escape codes for regular and fast vertical scroll
Windows Console Host	❌	❌	✅	❌	❌	only sends escape codes for regular and fast vertical scroll
VSCode	❌	❌	✅	❌	❌	only sends escape codes for regular and fast vertical scroll
mintty	✅	❌	✅	✅	❌	shift + vertical scroll moves the cursor up and down (???) and shift + alt + vertical scroll moves the current line up and down
Linux						(Arch with KDE on Wayland)
VSCode	❌	❌	✅	❌	❌	only sends escape codes for regular and fast vertical scroll
Alacritty	✅	✅	✅	✅	✅
COSMIC Terminal	✅	✅	✅	✅	✅	horizontal scroll wheel is inverted
Ghostty	✅	✅	✅	✅	✅	scrolls very fast with precision scrolling, but this seems to also be a problem in other command-line utilities that support mouse scrolling
GNOME Console	✅	✅	✅	✅	✅
GNOME Terminal	✅	✅	✅	✅	✅
kitty	✅	✅	✅	✅	✅
Konsole	❌	❌	❌	❌	❌	Holding shift while vertical scrolling doesn't change the scroll axis, and scrolling with horizontal scroll wheel does nothing except when holding alt which causes it to scroll vertically fast
LXTerminal	✅	✅	✅	✅	✅
MATE Terminal	✅	✅	✅	✅	✅
QTerminal	❌	❌	❌	❌	❌	Holding shift while vertical scrolling doesn't change the scroll axis, and scrolling with horizontal scroll wheel does nothing except when holding alt which causes it to scroll vertically fast
Xfce Terminal	✅	✅	✅	✅	✅
XTerm	✅	❌	✅	✅	❌	Doesn't send escape codes for shift + scrolling

Not tested:

• Mac OS

I didn't try any other terminal mouse tracking modes. For all I know, there may be one that gets more terminals to work, but changing it will probably mess up a whole bunch of other stuff.

Scrolling horizontally by 7 characters seems to be about the same as what VS Code does and fast scrolling is a 5x multiplier by default in VS Code. I wouldn't mind other people's opinions on these values though.

Cool project, BTW.