feat(riscv): select riscv.andn, riscv.orn, riscv.xnor

[regehr]

a few little things to note about this:

• I noticed that the unrealized conversion casts were making the code annoying so I made some helpers to add those with less boilerplate
• since the LLVM dialect code has passed our verifier, checking only one of (input1, input2, result) for width 64 suffices
• I moved our existing matchNot function to a shared file. note that it already expected the literal constant to be on the RHS, even before we had a canonicalizer

[github-actions]

VeIR Benchmarks

Details

Benchmark suite	Current: c9e45ea	Previous: cc0b571	Ratio
add-fold-worklist/create	2214000 ns (± 59245)	2245000 ns (± 59823)	0.99
add-fold-worklist/rewrite	4038000 ns (± 73583)	3943000 ns (± 62416)	1.02
add-fold-worklist-local/create	2147000 ns (± 80041)	2268000 ns (± 50000)	0.95
add-fold-worklist-local/rewrite	3294000 ns (± 95051)	3319000 ns (± 31736)	0.99
add-zero-worklist/create	2186000 ns (± 46408)	2235000 ns (± 108232)	0.98
add-zero-worklist/rewrite	2576000 ns (± 38940)	2508000 ns (± 31572)	1.03
add-zero-reuse-worklist/create	1823000 ns (± 89461)	1834000 ns (± 90486)	0.99
add-zero-reuse-worklist/rewrite	2136000 ns (± 36874)	2108000 ns (± 32722)	1.01
mul-two-worklist/create	2230000 ns (± 111447)	2248000 ns (± 109222)	0.99
mul-two-worklist/rewrite	5593000 ns (± 128558)	5544500 ns (± 143297)	1.01
add-fold-forwards/create	2205000 ns (± 57057)	2205000 ns (± 111151)	1
add-fold-forwards/rewrite	2981000 ns (± 47648)	2998000 ns (± 62583)	0.99
add-zero-forwards/create	2190000 ns (± 90386)	2291000 ns (± 81627)	0.96
add-zero-forwards/rewrite	1961000 ns (± 35682)	1903000 ns (± 92249)	1.03
add-zero-reuse-forwards/create	1861500 ns (± 92806)	1866500 ns (± 87239)	1.00
add-zero-reuse-forwards/rewrite	1569500 ns (± 45139)	1562000 ns (± 24410)	1.00
mul-two-forwards/create	2121000 ns (± 58845)	2189000 ns (± 55971)	0.97
mul-two-forwards/rewrite	3641000 ns (± 34113)	3612000 ns (± 88471)	1.01
add-zero-reuse-first/create	1841000 ns (± 79588)	1862000 ns (± 71721)	0.99
add-zero-reuse-first/rewrite	8000 ns (± 2644)	8000 ns (± 2593)	1
add-zero-lots-of-reuse-first/create	1899000 ns (± 36062)	1815000 ns (± 64825)	1.05
add-zero-lots-of-reuse-first/rewrite	802000 ns (± 16574)	785000 ns (± 22749)	1.02

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