Refactor/template calc service

[chrismclarke]

PR Checklist

• PR title descriptive (can be used in release notes)

Breaking Changes

The window.calc accessor has been marked as deprecated, e.g. @calc(window.calc.pick_random([1,2,3]))
Any methods available via window.calc.xxxx are already available directly, e.g. @calc(pick_random), so use that way instead.

I can't see any examples of this being used in example_calc, so assume this is mostly a legacy behaviour anyways

The only method that should still be accessed via the window is the date_fns utility library, e.g. @calc(window.date_fns.add_days(...))

Description

Changes merged from #2772 for easier review, a handful of updates to the template-calc.service which handles authored @calc(...) statements, specifically

Author Notes

Beyond the marked deprecation, there shouldn't be any breaking changes or functional testing required.

Review Notes

The code doesn't introduce changes to how calc statements are evaluated (for follow-up), so more just to confirm test cases behave as expected

Dev Notes

The changes introduced here should be mostly non-functional (testing, mock and type-safety improvements). The additional method included is designed for future integration in #2772, so in itself shouldn't be breaking.

Whilst diving into the service I did notice a handful of inconsistencies and clunky areas within the code, however have avoided larger refactor as would be best done through RFC procedures first (beyond marking window.calc as deprecated. Goals of a larger refactor would include:

• Improve ways to define deployment-specific calc functions
• Customisable list of 3rd party libs to include in calc (currently just date_fns included for all)
• Improved parser methods to extract globals required by calc statements and only including those when generating calc context

Git Issues

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[chrismclarke]

Rebase into #2793 for cleaner commits