Bitwig's official getting-started tutorial covers three keyboard-driven techniques for editing MIDI notes in the piano roll: transposing by semitone or octave, scaling note lengths, and applying Legato. All three can be accessed through the Note menu, but the faster routes are all on the keyboard.
For transposition, the arrow keys move selected notes up or down by semitone, and holding Shift jumps them a full octave. For scaling, holding Alt/Option while dragging the edge of a note or a selected range stretches or compresses the lengths, with the left edge of the range acting as the anchor point.
Legato extends each note's endpoint to meet the start of the next, closing any gaps in a single click. It's especially useful for pads and textures, or for cleaning up notes that came in slightly too short during recording.