Help: hyperlink $<_0> and configure-time commands in $<LIST> docs

Several $<LIST> doc references appeared as plain literal text: the bound
operand $<_0>, the configure-time list(TRANSFORM ... APPLY) command (the
TRANSFORM APPLY action title and prose), and the $<LIST:TRANSFORM,...,APPLY,body>
example in the $<_0> definition.  Use the :genex: and :command: roles so they
hyperlink to their definitions, matching the sibling canned actions and the
rest of the manual.

Issue: #27892