Fix documentation warnings generated by JavaDoc (NFC) (#3428)

Some C++ Doxygen comments were updated to reflect any wording changes.

See `rg "(@return|@param \w+) TODO" | less` for list of incomplete docs.

docs/build.gradle

@@ -68,10 +68,6 @@ doxygen {
     recursive true
     quiet true
     warnings false
-    warn_if_doc_error false
-    warn_no_paramdoc false
-    warn_format false
-    warn_logfile false
     warn_if_undocumented false
     generate_latex false
     use_mathjax true