`operator|` for range adaptor closure objects is not in the index

[t3nsor]

It is very difficult to find the place in the standard that specifies the semantics of R | C where R is a range, unless you already happen to know that C is called a "range adaptor closure object".

Under the top-level entry for operator| in the library index, there ought to be a subentry that says "range adaptor closure objects, [range.adaptor.object]" or something similar.

Relatedly, "range adaptor closure object" itself should be in the main index but is not.

[frederick-vs-ja]

Same for pipeable sender adaptor closure objects (specified in [exec.adapt.obj]).