Log Message:
tex-platex{,-doc}: update to 2020.57730

* Format date: pLaTeX2e <2020-10-01>+2.
* Adapt to LaTeX2e <2021-05-01> pre-release-1.

* Format date: `pLaTeX2e <2020-10-01>+1`.
* Improve rollback detection of new hook system.
* plext.sty: Support e-TeX length expressions in picture coordinates
  (similar to LaTeX2e 2020-10-01).