Scroll to the bottom of editor if on last line
Scroll to the bottom of editor if on last line

Make the MessageComposerInput scroll to the bottom if we are on the last line of the contents.

fixes https://github.com/vector-im/riot-web/issues/4652

matrix-org/matrix-react-sdk,matrix-org/matrix-react-sdk,matrix-org/matrix-react-sdk,aperezdc/matrix-react-sdk,aperezdc/matrix-react-sdk,matrix-org/matrix-react-sdk,matrix-org/matrix-react-sdk,aperezdc/matrix-react-sdk,aperezdc/matrix-react-sdk,matrix-org/matrix-react-sdk