cranelift-isle: no_std support

[the-ssd]

Part of #12222. Related to #1158.

Based on #9007, but made to always use no_std, just like discussed on the PR.

Because CI complained a lot when I tried adding extern crate alloc to the generated isle file, I instead added it to the tests. Wherever generated isle code is used must have access to alloc and core

[github-actions]

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