tests: Upgrade sendkeys, fix some bugs

[rhansen]

Multiple commits:

• tests: Fix helper.linesDiv()
• tests: Fix off-by-one bug in timeslider_follow.js
• sendkeys: Undo formatting and unnecessary changes
• sendkeys: Upgrade to oldest version in upstream repo
• sendkeys: Split into separate files to match upstream
• sendkeys: Merge in latest upstream commit that mostly works
• sendkeys: Fix \n to {enter} conversion
• sendkeys: Fix jQuery.fn.focus() return value
• sendkeys: Fix Range adjustment logic
• tests: Fix chat.js tests to accommodate new sendkeys
• ace2_inner: Get computed style of first Element, not first Node

[stale[bot]]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[stale[bot]]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[stale[bot]]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.