Allow custom mousemove conditions

When configuring a Select interaction with a custom condition that
includes mousemove, panning the map will not work any more. This is
because the return value of handleMapBrowserEvent is determined by
checking for a default condition function. By checking for the
underlying event type instead, we gain flexibility with custom condition
functions.
Merge pull request #3033 from ahocevar/select-return

Allow custom mousemove conditions for Select interaction