cranelift/egraphs: more select/bitselect optimizations

[jameysharp]

I've been thinking about the algebraic relationships between bmask and other instructions due to recent PRs, and wrote down a few of them here.

These patterns don't seem to appear in any of the Sightglass bz2, pulldown-cmark, and spidermonkey benchmarks, as this PR has no effect on execution-time instructions retired for those benchmarks.

[github-actions[bot]]

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