[script_tests] improve coverage of minimal number encoding

Summary:
It looks like the MINIMALDATA flag is destined to be a consensus rule so
it needs to be tested properly.

A couple of sections are labelled "Test every numeric-accepting opcode
for correct handling of the numeric minimal encoding rule" and a few
number-accepting opcodes have been added since then, so for completeness
the tests now include all number-accepting opcodes. Some of these are
redundant but it's good to have them all collected in one place.

(Also there was an oversight in one OP_NUM2BIN test which supposedly failed
due to nonminimal number, but actually failed due to too-long number. With
a shorter non-minimal number the test actually passes.)

Test Plan: make check

Reviewers: deadalnix, jasonbcox, Fabien, Mengerian, #bitcoin_abc

Reviewed By: deadalnix, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D3347