DevTools: [Elements] Implement shortcut-based node cut-copy-pasting

R=aandrey, pfeldman, vsevik
BUG=394384

Review URL: https://codereview.chromium.org/397303002

git-svn-id: svn://svn.chromium.org/blink/trunk@179031 bbb929c8-8fbe-4397-9dbb-9b2b20218538