Use new tests for S26
S26: Change #| to create leading declaration comments
S26: Remove leading comments from codebase

Leading comments currently break the build process (but work
otherwise), and I don't have the knowhow to fix it.  I'm
guessing it has something to do with BOOTSTRAP
Rename docs to leading_docs
Track preceding declarations
Implement trailing docs

It's pretty rudimentary at the moment, but it's a start:

  - Uses strings instead of objects
  - Only deals with package declarations
  - Doesn't deal with trailing blocks
Implement leading declarative comments for parameters
Set up trailing docs with DOCEE
Add traits for applying trailing decl docs
Use trait application for trailing decl docs

Using HOW.set_trailing_docs works for classes, but it
breaks down for routines because they all share a single
HOW, resulting in every Routine sharing the same trailing
docs
Track line numbers for routine declarations

This is necessary to implement trailing declarative docs
for routines
Track routines as potentials for trailing decl docs
Consider method definitions for trailing decl docs
S26: Implement leading docs for attributes
Implement trailing docs for Attributes
S26: Implement trailing comments for Parameters

This implementation is a little different from the others because
the actual parameter may not be created until after the trailing
comments have been parsed (because the latter is parsed as whitespace).
So we have to set up a "dummy" parameter and transfer the trailing
comments after the fact.  I also didn't use an anonymous role to
store the trailing docs, because it was easier to extract them from
the dummy, should they exist at all.
Clear DECLARATOR_DOCS immediately after use
Specify leading or trailing for Perl6::Pod::document
S26: Don't invoke apply_traits manuall for leading docs
Use Perl6::Pod::document for trailing docs too