DOC: Fix `vtk::ExtractSelectedPolyDataIds` class doc inline code markup
Fix vtk::ExtractSelectedPolyDataIds
class doc Doxygen inline code
markup: use backticks to for an inline span of code.
Prefer them over the \verbatim
/\endverbatim
commands used in commit
93741a95 as these start a new paragraph.
Documentation: https://www.doxygen.nl/manual/markdown.html#md_codespan