Embedded Racc runtime is exposed as part of RDoc's generated API documentation

[thyresias]

Description

RDoc's generated RD parsers contain a complete embedded copy of the Racc
runtime:

lib/rdoc/rd/block_parser.rb
lib/rdoc/rd/inline_parser.rb

In both files, the embedded section is delimited by:

###### racc/parser.rb begin

and:

###### racc/parser.rb end

RDoc parses this embedded implementation as if it were part of RDoc's public
API. As a result, generating RDoc's own documentation creates a Racc module
page.

The embedded comments also contain this reference:

rdoc-ref:lib/racc/rdoc/grammar.en.rdoc

It produces two unresolved-reference warnings, one from each generated
parser:

classes/Racc.html: `rdoc-ref:lib/racc/rdoc/grammar.en.rdoc` can't be resolved
classes/Racc.html: `rdoc-ref:lib/racc/rdoc/grammar.en.rdoc` can't be resolved

Relevant generated files:

https://github.com/ruby/rdoc/blob/v8.0.0/lib/rdoc/rd/block_parser.rb

https://github.com/ruby/rdoc/blob/v8.0.0/lib/rdoc/rd/inline_parser.rb

Expected behavior

The embedded Racc runtime is an implementation detail of the RD parsers. It
should not create Racc, Racc::Parser, or related pages in RDoc's API
documentation.

The actual RDoc classes defined after the embedded section, such as
RDoc::RD, must remain documentable.

Suggested fix

Wrap the embedded runtime in RDoc exclusion directives:

# :stopdoc:
###### racc/parser.rb begin

# Embedded Racc runtime

###### racc/parser.rb end
# :startdoc:

This must be integrated into parser generation or its post-processing, since
the generated .rb files are committed and regenerated from the .ry
sources.

I tested these directive positions:

• Racc is no longer added to the documentation store;
• RDoc::RD remains documented;
• the two unresolved references disappear.

A regression test could parse both generated files and assert:

refute store.find_class_or_module("Racc")
assert store.find_class_or_module("RDoc::RD")