Meta-ticket: Improvements of the editable install of sagelib

[mkoeppe]

Following up on #31377.

• "setup.py develop" rewrites the installed sage-version.sh as if it is a Python script #31049 setup.py develop rewrites the installed sage-version.sh as if it is a Python script
• Remove sage-gdb-commands from src/bin #33627 Move sage-gdb-commands out of src/bin
• Make "./configure --enable-editable" the default #32406 Make ./configure --enable-editable the default
• progress report, how many files yet need to be compiled
• Source dir cleaner for editable installs #34334 a version of sage_setup.clean.clean_install_dir for editable installs: remove .so and .pyc files that are leftovers from other branches
• Don't hardcode nthreads=4 for cythonizing but use the one used by make and/or SAGE_NUM_THREADS. See also Unify computation of number of parallel jobs #33317.
• (from #32406 comment:24): upon startup, automatically detect if it had to recompile because of a change to a Cython file and issue a warning
• Modern editable installs (PEP 660) #38439 (Use PEP 660 editable wheels for sagelib #34209)

CC: @kliem @tobiasdiez

Component: build

Issue created by migration from https://trac.sagemath.org/ticket/31406

[mkoeppe]

comment:4

Sage development has entered the release candidate phase for 9.3. Setting a new milestone for this ticket based on a cursory review of ticket status, priority, and last modification date.