Reintroduce workspace inheritance

[jimblandy]

In #3295, we had to remove the use of workspace inheritance from wgpu, because of rust-lang/cargo#11192. It seems like rust-lang/cargo#11414 has fixed the problem, so we should try re-introducing inheritance and see how that goes.

[jimblandy]

Mozilla is tracking this in Bugzilla 1804530.

[teoxoy]

The version of cargo with the fix will be part of rust 1.68, scheduled for 9th March. We also need to wait for mozilla-central to upgrade.

[jimblandy]

Confirmed that Cargo 1.68 does indeed fix this.

At the moment, Firefox 115's MSRV is Cargo 1.66, so we still need to wait a little longer.

[cwfitzgerald]

@jimblandy could you link again where we can tell ff's msrv? Would like to add it to our own documentation.

[jimblandy]

https://firefox-source-docs.mozilla.org/writing-rust-code/update-policy.html

[jimblandy]

It seems like the MSRV in Firefox is now 1.70, so maybe we can fix this:
https://searchfox.org/mozilla-central/source/python/mozboot/mozboot/util.py#14