Hover API improvements

[Tyriar]

Notes after talking about this in a UX sync:

• Add section to UX guidelines for hover vscode-docs#8135
• hideOnKeyDown: true should be the default? Maybe we don't need it at all?
• compact: true is a special case, we need clear guidelines to follow
• Add hoverPosition: 'horizontal' | 'vertical' which should render forcePosition maybe obsolete completely and simplify usage
• Change showHover to showInstantHover, and showDelayedHover* to showHover*?
  • showHover -> showInstantHover showHover -> showInstantHover #243349
  • showDelayedHover -> showHoverAtText (aligning with text should be a special case not the default)
  • showDelayedHoverAtMouse -> showHoverAtMouse
  • showDelayedHover will default showPointer: true?