Exported range_inclusive in the prelude

[gereeter]

There are several examples I've noticed of people using range with an upper bound one larger than what the really want to simulate an inclusive range, the ones I remember at the moment being these two Rust by Example pages. Moreover, there has recently been some confusion about the lack of an inclusive range. This seems to be a general problem of people not realizing that range_inclusive exists. Therefore, in hopes of making it more visible and easier to use, this PR puts it the prelude. This allows the Rust by Example pages to switch to using the more readable range_inclusive without having to introduce use first.

[emberian]

Per the meeting, we've decided that the prelude should only be used for overwhelmingly pervasive functions, and range_inclusive just does not fall into that bucket.

As my own comment on top of that, putting something in the prelude doesn't make something more visible, just easier to use. I don't find the RbE argument particularly compelling since merely introducing a use of use isn't that difficult, if it wants to use range_inclusive.