Split support

[raphamorim]

This PR introduces split and also a major rewrite of the renderer to increase performance by avoiding redundancy in render operations.

TODO:

• Each rich should respect it's own pos
• Each rich text have it's own layout
• Erase line
• Replace line content
• Move terminal content to context level
• Replace Context with GridContext
• Fix issue whenever dpi changes
• IME/Cursor should be rendered based on it's own context
• Fix cursor shape update through configuration
• Add SplitRight
• Add SplitDown
• Add SelectNextSplit
• Add SelectPrevSplit
• Add CloseSplitOrTab
• Add resize support
• Selection isn't working correctly
• Add key bindings for Linux/Windows
• Update docs regarding actions

Will move to a different PR

• Add SplitHighlight (all other panels get lower opacity)
• Add SplitFocus (hide all other panels and increase current one)

Sugarloaf example

Ref #184

[raphamorim]

Resize for reference