Documentation: Input leadingcontent wrong with Angular

[ArakTaiRoth]

Acceptance Criteria:

1. In our properties block for the Input component for Angular, leadingcontent and trailingcontent should be changed to leadingContent and trailingContent respectively
2. All of our examples that use leadingContent and/or trailingContent need to be redone, as currently the code provided doesn't work. It needs to be changed to use the slot.
3. Expand our React documentation to show how to use the ReactNode for leadingContent and/or trailingContent rather than just text