* Merge RubyGems-3.5.12 and Bundler-2.5.12

* Merge RubyGems-3.5.13 and Bundler-2.5.13

* Merge RubyGems-3.5.14 and Bundler-2.5.14

* Merge RubyGems-3.5.15 and Bundler-2.5.15

* Merge RubyGems-3.5.16 and Bundler-2.5.16

https://github.com/rubygems/rubygems/commit/bb66253f2c

https://github.com/rubygems/rubygems/commit/93619c97ff

This gets the specs passing, and handles the fact that we expect
checkums to be pinned only to a particular source

This also avoids reading in .gem files during lockfile generation,
instead allowing us to query the source for each resolved gem to grab
the checksum

Finally, this opens up a route to having user-stored checksum databases,
similar to how other package managers do this!

Add checksums to dev lockfiles

Handle full name conflicts from different original_platforms when adding checksums to store from compact index

Specs passing on Bundler 3

https://github.com/rubygems/rubygems/commit/86c7084e1c

  from https://github.com/rubygems/rubygems/commit/0635c1423db5d7c461d53bf0c3329bca75de7609

RubyInstaller has released patch versions backporting their changes to
not load `fiddle` on boot, so all these are no longer necessary.

https://github.com/rubygems/rubygems/commit/05a307deb2

When testing under the ruby/ruby setup, mkmf.rb needs to the `$extout`
global variable set properly.

This is because, in this particular case, the `ruby.h` header needed to
compile extensions is constructed from
`$(extout)/include($arch)/ruby/config.h` but `$extout` is not set by
default.

I tried to fix this in mkmf.rb itself but I couldn't figure it. But
setting it externally to workaround the issue fixes the specs, so I'll
start with that. Also setting it externally causes issues when running
specs upstream against Ruby 2.3 (I guess because of some difference with
Ruby 2.3 mkmf.rb implementation). So I'm avoiding doing it on Ruby 2.3 to
woraround that.

https://github.com/rubygems/rubygems/commit/d782984585

https://github.com/rubygems/rubygems/commit/70ff7cee9f