Fix foreign docs in several places

[lambdadog]

Consolidation of #647, #648, and #649 + a LOG entry.

• Slocked_objectp is now named correctly, as opposed to the previous incorrect Sunlocked_objectp.
• Correctly marked Sforeign_callable_{entry_point,code_object} as macros, rather than functions.
• Correctly marked Ssymbol_to_string as a function, rather than a macro.

[lambdadog]

Does this look correct, @jltaylor-us?

[jltaylor-us]

I would probably be a little more specific in the LOG, like

fix some C functions mislabeled as macros and vice-versa,
Slocked_objectp misspelled as Sunlocked_objectp

but the only real issue is the missing newline at the end of LOG. (Might as well keep the tools from whining about it.)

[lambdadog]

I can absolutely be more specific.

[jltaylor-us]

Thanks again!