Improve Clickable and Input Component

[ericluap]

Some ideas for improving the functionality of the Clickable and Input component:

• Clicking inside of an input should change the cursor position on mouse down, not mouse up.

• The cursor should still be captured by the input when it leaves the input so that highlighting text can work well.

For Clickable (possibly unnecessary):

• Clickable should use Hooks.mouseCapture instead of its own mouse capture system

• Mouse down on a clickable, leaving the clickable, re-entering the clickable, and then mouse up back on the clickable should still count as a click.
  In other words, if the mouse down and mouse up occur on the clickable, it should not matter if the cursor left.