Improved readability of negative condition in makemessages

Thanks Berker Peksag for the suggestion.
Added assertion error message for test_make_line

Refs #23842. Thanks Thomas Chaumeny for the suggestion.
Fixed #20435 -- Reordered the custom template tags docs.

Introduced the various shortcuts before explaining the more complex
parser/render functionality.

Also removed non-decorator syntax: it's been years since Django
supported a Python version without decorators.
Moved bilateral transform fetching to models.lookups
Fixed #23855 -- Removed unnecessary all() in tutorial 3.
Reordered condition to avoid calling allow_migrate() if unneeded.
Avoided unneeded calls to state.render() in migrations.
Fixed #23859 -- Fixed a migration crash when a field is renamed that is part of an index_together
Merge pull request #3563 from MarkusH/ticket23859

Fixed #23859 -- Fixed a migration crash when a field is renamed that is part of an index_together
Removed superfluous newline.
Normalized check that ALLOWED_INCLUDE_ROOTS is a tuple.
Adjusted tests for previous commit.

The test was testing a use case that doesn't happen in real world
projects: developers don't assign settings at run time (and Django
explicitly doesn't support it).
Fix link target markup

This markup for a code block is redundant with the code-block directive below,
and blocks the following line from working as link target.
Fix malformed note directives.
Fixed #23799 -- Made makemigrations respect --no-optimize.

Thanks to yamila-moreno for the idea of a skip message.
Fixed #18714 -- Added 'fuzzy' compilemessages option
Deprecated calling a SQLCompiler instance.
Fixed #23849 -- Documented the locmem.Loader class.
Removed nonexistent module django.test._doctest from coveragerc.
Fixed #22248 -- Made RenameModel reversible