Closes #7818

I think of this as a stylistic opinion which shouldn't necessarily be enforced
by default on all users of rust, but that's just my opinion.

Also ends up fixing one case in libstd

is very common, and the replacement (.iter().transform().collect()) is very
ugly.

Mostly just low-haning fruit, i.e. function arguments that were @ even
though & would work just as well.

Reduces librustc.so size by 200k when compiling without -O, by 100k when
compiling with -O.

I removed the `static-method-test.rs` test because it was heavily based
on `BaseIter` and there are plenty of other more complex uses of static
methods anyway.

The removed test for issue #2611 is well covered by the `std::iterator`
module itself.

This adds the `count` method to `IteratorUtil` to replace `EqIter`.

This almost removes the StringRef wrapper, since all strings are
Equiv-alent now. Removes a lot of `/* bad */ copy *`'s, and converts
several things to be &'static str (the lint table and the intrinsics
table).

There are many instances of .to_managed(), unfortunately.

Add some more cases for warning about missing documentation, and also add a test
to make sure it doesn't die in the future.