[v8.x] src: move `Environment` ctor/dtor into env.cc
This makes it easier to use methods from other headers in the constructor and destructor.
PR-URL: https://github.com/nodejs/node/pull/19202
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