Build is broken by pgf bug

[paolobrasolin]

Versions 3.1 and 3.1.1 of pgf have a bug which makes them incompatible with engines missing etex extensions. Specifically, \scantokens.

More informations here: https://tex.stackexchange.com/q/473365/82186

The bug (known) was introduced by ac33f7 while fixing #306. It was solved by 287814, 46eaad, and 4abefd thus closing #508.

The solution amounts to a generalization of this old shim. The shim essentially is

\long\def\scantokens#1{#1}

TODO

• [x] temporarily patch the build with the shim
• [ ] remove the shim from the build framework once pgf > 3.1.1is released
• [ ] add note in the documentation about using the shim before \inputing kodi if no etex extensions are available
• [x] remove the shim from the build framework and abandon tex in favour of etex
• [ ] add note in the documentation about etex

[paolobrasolin]

Henri decided do make eTeX a hard requirement with https://github.com/pgf-tikz/pgf/commit/187f5f484720100c9cfab49aa90832c2b2fcc6c1

I definitely can't blame him.