gh-36747: `build/bin/sage-spkg`: Add support for installing script packages
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Split out and updated from #29386.
The section of `build/make/Makefile.in` that deals with script packages
can be consolidated with the section on normal packages later, in a
follow-up PR after #36740, #36738.
We switch the `spkg-install` scripts of the `sage*` script packages to
the templated versions (`spkg-install.in`), which is a simplification.
`spkg-check` remains as is because we still invoke it directly (changing
this will need #36738).
Resolves #29386.
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### :hourglass: Dependencies
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- Depends on #36737 (for testing)
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URL: https://github.com/sagemath/sage/pull/36747
Reported by: Matthias Köppe
Reviewer(s): Michael Orlitzky
