Fall back to AllSelection in Selection.near/atStart/atEnd
Fall back to AllSelection in Selection.near/atStart/atEnd

FEATURE: [`Selection.near`](##state.Selection^near),
[`atStart`](##state.Selection^atStart), and
[`atEnd`](##state.Selection^atEnd) will now fall back to returning an
[`AllSelection`](##state.AllSelection) when unable to find a valid
selection. This removes the (undocumented) requirement that documents
always contain a valid selection position (though you'll probably
still want to maintain this for practical UI reasons).

BREAKING: [`Selection.atStart`](##state.Selection^atStart), and
[`atEnd`](##state.Selection^atEnd) no longer take a second `textOnly`
parameter.

ProseMirror/prosemirror-state