Fixed inconsistent usage of keep_local and local_only kwarg in Help() function, its implementation and docs

[hedger]

Contributor Checklist:

• I have created a new test or updated the unit tests to cover the new/changed functionality.
• I have updated CHANGES.txt (and read the README.rst)
• I have updated the appropriate documentation

[bdbaddog]

Not sure why you beleive this change is needed?
local_only, means only the local addoptions args are in the help.. what's the concern here?

[hedger]

@bdbaddog the concern is that documentation is inconsistent with actual behavior.

Currently, the docs mention the following prototype for the Help() function:

env.Help(text, append=False, local_only=False)

While actual implementation in

scons/SCons/Script/__init__.py

Line 254 in 4f3e302

def HelpFunction(text, append: bool = False, keep_local: bool = False) -> None:

uses the keep_local kwarg name.

I made the documentation consistent with the actual implementation - in order to not break any third-party code that relies on existing behavior. I also renamed the kwarg inside the implementation to avoid confusion.

[bdbaddog]

Seems like it would be simpler to just make everything local_only and not keep_local

also calling Help() in your SConscript calls SCons.SConscript.Help(), and not PrintHelp() (not directly).
Help() calls HelpFunction() which calls PrintHelp()

So the public interface is SCons.SConscript.Help(), and that's what's misdocumented.
(and mis doc-string'ed too I think)

Thoughts @mwichmann ?