Make circuit rendering of swap-like gates consistent

[viathor]

The PR makes layout and capitalization of swap-like gates consistent.

Before:

In [3]: cirq.Circuit(cirq.PhasedISwapPowGate().on(q0, q1), cirq.ISwapPowGate().on(q0, q1), cirq.FSimGate(0, 0).on(q0, q1))
Out[3]: 
0: ───PhISwap(0.25)───iSwap───fsim(0, 0)───
      │               │       │
1: ───PhISwap(0.25)───iSwap───#2───────────

After:

n [3]: cirq.Circuit(cirq.PhasedISwapPowGate().on(q0, q1), cirq.ISwapPowGate().on(q0, q1), cirq.FSimGate(0, 0).on(q0, q1))
Out[3]: 
0: ───PhISwap(0.25)───ISwap───FSim(0, 0)───
      │               │       │
1: ───PhISwap(0.25)───ISwap───FSim(0, 0)───

[viathor]

This also changes "swap" to "Swap" when unicode isn't being used.

[Strilanc]

i refers to sqrt(-1), I refers to Identity. It really is an iSwap in my opinion. Not sure if the consistency benefits are worth it in the diagrams.. Opinions? It's certainly a bit odd that in the code it gets capitalized if it doesnt in the diagrams.

[viathor]

Reverted back to iSwap with the small i. PTAL.

[viathor]

PTAL