classes/crate-fetch: Ensure crate fetcher is available

Reworks the crate fetcher class to have it install the fetcher at recipe
finalization so that it is always available before SRC_URI is expanded.
In addition, override the value of SRCPV to also install the fetcher
when SRCPV is expanded so that AUTOREV works.

[YOCTO #10867]

Signed-off-by: Joshua Watt <JPEWhacker@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>