Order of rewrites is only respected if kwarg position is used

[ricardoV94]

I could be wrong, but when working on pymc-devs/pymc#6072, it seemed that the order of the rewrites in the database is only respected when using the kwarg position. Otherwise it seems to be ignored, and only the order of definition matters.

So:

aeppl/aeppl/rewriting.py

Lines 234 to 236 in 8ce3c63

	logprob_rewrites_db.register(
	"measurable_ir_rewrites", measurable_ir_rewrites_db, -10, "basic"
	)

Should be:

logprob_rewrites_db.register( 
     "measurable_ir_rewrites", measurable_ir_rewrites_db, "basic", position=-10, 
 )

[ricardoV94]

We should probably also leave an offset between pre-canonicalize and measurable_ir_rewrites (both are supposed to be at -10) in case anyone wants to introduce rewrites between those two phases.