Python: Allow type tracking through comprehensions

[yoff]

• the subscript operator is extended to comprehensions
• the capture jump-step is extended to work for the functions generated inside comprehensions

Pull Request checklist

All query authors

• A change note is added if necessary. See the documentation in this repository.
• All new queries have appropriate .qhelp. See the documentation in this repository.
• QL tests are added if necessary. See Testing custom queries in the GitHub documentation.
• New and changed queries have correct query metadata. See the documentation in this repository.

Internal query authors only

• Autofixes generated based on these changes are valid, only needed if this PR makes significant changes to .ql, .qll, or .qhelp files. See the documentation (internal access required).
• Changes are validated at scale (internal access required).
• Adding a new query? Consider also adding the query to autofix.

[yoff]

Possibly a small performance penalty, but reasonable for the added flow:

source	a_m	a_std	b_m	b_std	diff	relative
Median (excl. partials)					1	0.0156
Overall (excl. partials)	3944		3969		25	0.00634

[tausbn]

Looks good to me! Thanks for the quick chat about jump steps.