Add remaining single qubit Clifford gates

[Strilanc]

Add the last 9 (out of 24) single qubit Clifford gates that weren't defined by stim until now:

• Add C_NXYZ gate
• Add C_XNYZ gate
• Add C_XYNZ gate
• Add C_NZYX gate
• Add C_ZNYX gate
• Add C_ZYNX gate
• Add H_NXY gate
• Add H_NXZ gate
• Add H_NYZ gate

Also add some useful placeholder gates for the tag-obsessed to use:

• Add I_ERROR gate
• Add II_ERROR gate
• Add II gate

And finally some compatibility changes:

• Modify crumble to replace feedback gates with "ERR" gates, instead of silently removing them
• Generalize crumble's 'k+#' automark functionality to work with multi-qubit measurements
• Modify stimcirq to turn all cirq.SingleQubitCliffordGate instances into a single gate, instead of ever using multiple gates

Fixes #885

Fixes #855

[Strilanc]

@m-mcewen