nir,microsoft: Move scale_fdiv into a common NIR pass

While we're at it, convert to nir_shader_instructions_pass() to get rid
of some boilerplate and get metadata correct.

Reviewed-by: Jesse Natalie <jenatali@microsoft.com>
Part-of: <!15983>
184 jobs for !15983 with nir/scale-fdiv in 57 minutes and 47 seconds (queued for 7 seconds)
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