gdscript highlighting and packaging

[DavidCooperWCU]

A new prism format was added for gdscript 2.0
A new component was added to generate gdscript packs as zip files The documentation was updated to describe the new gdscript highlighting and active code capabilities 1 program example and 3 activecode examples were added to the Runestone Testing section of the sample book.

[DavidCooperWCU]

To test this:

1. checkout the pr with gh pr checkout 3024
2. cd examples/sample-book
3. mkdir out-test
4. python ../../pretext/pretext -vvv -d out-test -f html -c all -p publication-structural.xml sample-book.xml
5. mkdir out-test/generated/gdscript
6. python ../../pretext/pretext -vvv -d out-test/generated/gdscript -f html -c gdscript -p publication-structural.xml sample-book.xml

Then serve the book and look at Listing 5.1.3 to see the godot highlighting.

Activities 5.2.1, 5.2.2, and 5.2.3 are examples how the ActiveCode will look, but it won't work fully until rs - PR 1233 has been accepted.

This is a circular dependency, but this PR is the first step.