[vm] Allow access to native extensions via the session. #293_162

[sahithiacn]

Motivation

Until now this have been hidden inside the session and only accessible from within native functions. This makes them also accessible outside so we can work with them on session level (e.g. for lazy code loading).

Have you read the Contributing Guidelines on pull requests?

Yes

[sahithiacn]

/canary

[bors-diem]

:sunny: Canary successful

[sahithiacn]

/land