doc,vm,test: remove _sandbox_ from vm documentation
The vm documentation uses the word sandbox but has a significant disclaimer about how that should not be interpreted to connote security guarantees. Remove the term "sandbox" from documentation. As a result, some code and tests also need to change.
Checklist
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make -j4 test
(UNIX), orvcbuild test
(Windows) passes -
tests and/or benchmarks are included -
documentation is changed or added -
commit message follows commit guidelines