Stricter javadoc parsing

Previously turbine was saving javadoc comments and associating them with the
parsed declaration that javadoc could be applied to, which was incorrectly
adding comments from skipped declarations (e.g. anonymous or local classes) to
unrelated declarations.

This change updates the lexer so javadoc comments have to be retrieved at the
same time as the next non-comment token, and updates the parser to check for
comments at the expected location for the documented declaration.

PiperOrigin-RevId: 874712509

Author: cushon