Coding Standards: Add visibility to methods in src directory.

[costdev]

Coding Standards: Add visibility to methods in src directory.

"Visibility should always be declared"
See: https://make.wordpress.org/core/2020/03/20/updating-the-coding-standards-for-modern-php/

This commit applies the following sniffs to files in src:

• Squiz.Scope.MethodScope
• PSR2.Methods.MethodDeclaration
• PSR2.Classes.PropertyDeclaration
• Squiz.WhiteSpace.ScopeKeywordSpacing

For all methods, these now indicate public visibility to avoid breaking backwards compatibility.

Trac ticket: https://core.trac.wordpress.org/ticket/54177

[jrfnl]

Ready for commit.

All methods which did not have an explicit visibility have now been made public.

This is the correct visibility as no visibility implicitly makes a method public and, even though some methods may have been marked as "private" in the docblock, as the methods did not have visibility before, making these explicitly private would be a backward compatibility break, so public is the right choice for all these methods.

[hellofromtonya]

Committed via changeset 51919.