The reader tries to parse the rest of the opening line of a block, e.g.,
`#+begin_myblock …`, as a parameters list. It first assumes that the parameters
are in lisp-style (`:key value`), then alternatively tries to read python-style
key-value pairs (`key=value`) and falls back to reading the entire remaining
line as a single `parameter` attribute.
This method is also applied to dynamic blocks.
Closes: #11188
