This deduplicates argument handling logic from Help and man and makes it
more modular for future use cases. The argument handling works as
before: two arguments specify section and page (in this order), one
argument specifies either a page (the first section that it's found in
is used) or a path to a manpage markdown file.
- Calculate the full name on demand
- Make section and name protected
- Reorder some members logically
- Change the name getter to be fallible, as some implementors need to
allocate
This is a first step in deduplicating code within and across Help and
man.
Because LibManual also doesn't contain any DeprecatedString, some
adjustments to Help's string handling is included, just to interoperate
with LibManual better. Further work in this area mostly requires String
APIs in LibGUI.
