Generate list of symbols for autoloading at build-time

[ehuelsmann]

Currently, our list of symbols to be set up for auto-loading is
a manual maintenance effort which makes ABCL fragile with respect
to refactoring.

My idea would be to have an auto-collected list, with two (hand-coded) lists: one to include additional symbols and the other to exclude symbols (e.g. to reduce the size of the symbol list).

[ehuelsmann]

(In [14035]) Fix #226 (Invocation of an undefined function in a fresh ABCL crashes):
make sure the PRINT-OBJECT generic function exists
before defining methods on it.

[ehuelsmann]

r14035 solves #227, not this one.

[ehuelsmann]

(In [14036]) Re #226: Automatically generate autoloads.

This commit adds the auto generation code and infrastructure. Next steps
include clean up of autoloads.lisp, deciding how to handle symbols in
multiple files and SETF functions/expanders.

[ehuelsmann]

(In [14100]) Re #226: Clean symbols from manually maintained autoloads.lisp

which are also automatically detected by the automatic autoloader.

[ehuelsmann]

Next step:

Move EXPORT forms to the respective source files
defining the function and macro bindings.

[ehuelsmann]

We're nearly there: I noticed we don't detect structure slot accessors when
compiling the macro expansion of a defstruct, due to its use of SETF SYMBOL-FUNCTION.

Expanding to FSET and detecting that at compile-time would solve it.

[ehuelsmann]

(In [14126]) Closes #226: All exports and all but one autoload have been removed
from autoloads.lisp due to automatic loading. Documentation inside
autoloads.lisp has also been updated.

[ehuelsmann]

FSET detection can always be added later. For now, I'm assuming structures will be created before being accessed, meaning I'll rely on timely initialized accessors for now.