Add initial det/obs support to crumble, plus other polish

[Strilanc]

Tagalong Stim diagram improvements:

• Change 3d matchgraph diagrams to use a slightly more 3d indicator for detectors
• Change matchgraph diagrams to not decompose if decomposition produces any errors
• Change matchgraph diagrams to draw hypererrors that flip an observable in purple, instead of in blue

Crumble improvements:

• Fix hitting 1-9 on an MPP operation not inferring that it should mark every target of the operation in their basis

• Add initial support for detectors

  • d+# to turn a marked flow into a detector
  • o+# to turn a marked flow into an observable
  • Draw detecting regions of dets and obs as small squares on qubits at each moment in the timeslice, and between moment in the timeline
  • j+# to pick an arbitrary det or obs with a detection region going through the current selection, and turn it into a
  • k+# to add markers to dissipative gates overlapping the propagating flow in the current layer marked flow

• Fix feedback operations not being correctly ignored, or causing non-feedback parts of an operation to be discarded

• Polish the scrubber

  • Move it to run horizontally along the timeline
  • Add visual hints of what's in each layer

• Polish the visuals

  • Improve the indication of marker flows beyond 4
  • Make timeline view justify left when near start of circuit, and justify right when near end of circuit, to always show as much information as possible
  • Only show timeline-to-timeslice qubit position indicators when hovering over that qubit in the timeline
  • Fade out unused qubits more
  • Set the default polygon alpha lower, so they are more faded
  • Fix several instances of fuzzy drawing due to off-by-0.5 coordinates
  • Draw example polygons and markers in the toolbox to better indicate what P and # do

• Add quality of life controls

  • Fix needing to often hit cltr+z twice in order to undo once
  • Fix clicking on an example circuit link resulting in the undo history being lost
  • Press F to flip two qubit gates (e.g. exchange target and control)
    • Moved C_XYZ gate from F to c+t
  • Press G to reverse the order of layers starting from the current layer ending at first empty layer
  • Press >, <, ^, v to translate coordinates in the indicated direction
  • Press . to translate circuit downright one half step
  • Press home/end to jump to start/end of circuit
  • Press shift+q/e to jump 5 layers at a time

• Added more example circuits, and moved examples behind a "show examples" button

• Fix frame gate methods targeting indices instead of targets

• Add frame undo gate methods

• Fixes https://github.com/quantumlib/Stim/issues/771

• Fixes https://github.com/quantumlib/Stim/issues/715

• Fixes https://github.com/quantumlib/Stim/issues/738