Add a setting to control the vertical and horizontal scroll sensitivity

[carterols]

Some people (like myself) use touchpads for development and I find Zed's default scroll sensitivity to be slower than I like. This change adds a scroll sensitivity multiplier that allows users to customize the speed of their scrolling.

Release Notes:

• Added a setting under "scroll_sensitivity" that allows user to control the scroll sensitivity. This value acts as a multiplier for the horizontal and vertical scroll speed.

[cla-bot[bot]]

We require contributors to sign our Contributor License Agreement, and we don't have @carterols on file. You can sign our CLA at https://zed.dev/cla. Once you've signed, post a comment here that says '@cla-bot check'.

[carterols]

@cla-bot check

[cla-bot[bot]]

The cla-bot has been summoned, and re-checked this pull request!