ApplyFirstRemarkableOverFactors​(AngouriMath.​Entity,​AngouriMath.​Entity.​Variable,​AngouriMath.​Entity)

The rule matches a product or a quotient whose own child is a vanishing sine, so a
constant factor written to the left pushes that sine one level down and out of
reach: 2 * sin(1/x) * x parses as (2 * sin(1/x)) * x, whose children
are a product and a variable. The descent then reads it as 0 * (+oo) and is
definite about it, while the same product written sin(1/x) * x * 2 answers 2.
Which side a caller writes a constant on is not a mathematical difference, and
simplification produces either.
**Not a plain Replace, and that is the whole of what keeps it sound.** The
equivalence holds for a *factor* of the expression as a whole -- if f/g -> 1 then f*h and g*h go to the same place -- and not for a term of a sum,
where the difference between f and g is the entire answer. Rewriting
the sine inside (sin(x)/x - 1)/x^2 would answer 0 where the limit is -1/6.
Stopping at anything that is not a product or a quotient keeps every rewrite to a
factor of the whole.
#749