As a follow-up to #29053, we move the build/pkgs/*.txt files to a more systematic location. This will simplify some scripts.

• build/pkgs/_prereq/distros/debian.txt etc. - records the minimal requirements (system packages) for installing from source. (we move the current build/pkgs/debian.txt etc. there)
• build/pkgs/_bootstrap/distros/debian.txt etc. - would record the additional requirements for running ./bootstrap (we move the current build/pkgs/debian-bootstrap.txt there)

Related:

• Add script-type _spkg_check package that installs tox, mock, pytest etc. #28998: Add script-type _spkg_check package that installs tox, mock, pytest etc.
• Add script package _recommended and generate "recommended system packages" info #29557: build/pkgs/_recommended - records additional recommended packages such as texlive-xetex (see https://wiki.sagemath.org/prerequisites/Ubuntu)

Possible follow-up:

• build/pkgs/_toolchain/dependencies - to replace some special Makefile targets currently in build/make/Makefile.in.

Depends on #30940
Depends on #29655

CC: @dimpase @egourgoulhon @jhpalmieri @kiwifb @tobiasdiez @seblabbe @slel @kliem

Component: build

Keywords: sd111

Author: Matthias Koeppe

Branch/Commit: e8da106

Reviewer: Sébastien Labbé, Dima Pasechnik

Issue created by migration from https://trac.sagemath.org/ticket/29124