Fix/2919 type exports (export the static functions manually)

[josdejong]

Fix #2919 using the approach of Maxim worked out in #2932.

Changes:

• Renamed MathJsStatic into MathJsInstance
• The dependencies are no longer exported in MathJsInstance (they are not exported there in reality)
• Export all functions and constants of MathJsInstance as static constants.
• Document how to properly define types in types/EXPLANATION.md

To do:

• Bring the types up to date with all changes done in the v12 branch
• Test thoroughly

[josdejong]

Oops I hadn't realized that renaming the branch would close this PR.

Created a new PR: #3079