src: change env.h includes for forward declarations

Due to how the Environment class is used through the codebase,
there are a lot of includes referencing either env.h or env-inl.h.
This can cause that when any development touches those libraries,
a lot of files have to be recompiled.
This commit attempts to change those includes by forward declarations
when possible to mitigate the issue.

Refs: https://github.com/nodejs/node/issues/27531

PR-URL: https://github.com/nodejs/node/pull/30133


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
Reviewed-By: David Carlier <devnexen@gmail.com>
Reviewed-By: Franziska Hinkelmann <franziska.hinkelmann@gmail.com>