Add padding to View component

[noituri]

Snapshot tests: membraneframework-labs/video_compositor_snapshot_tests#52

The padding behavior:

• Static children:
  • If the size is defined for the child, grow the child's size by its padding, and offset its position with parent padding
  • If the size is not defined, shrink the child to accommodate the parent's padding, and offset its position with the parent's padding
• Absolute children:
  • If the size is defined for the child, grow the child's size by its padding
  • Parent padding does not affect its absolute children

Closes #926