docs: Document the DataTable and DocString step argument types

[Amoifr]

Documents the DataTable and DocString step argument types added in Behat/Behat#1864, which @acoulton asked for as a follow-up.

The two sidebars of "Multiline step arguments" now show the new types, since they are what a reader should reach for:

-use Behat\Gherkin\Node\TableNode;
+use Behat\Step\DataTable;

 #[Given('the following people exist:')]
-public function thePeopleExist(TableNode $table)
+public function thePeopleExist(DataTable $table)
 {
-    foreach ($table as $row) {
+    foreach ($table->asMaps() as $row) {

For tables the accessors are worth listing, because which one to use depends on the shape of the table and that is not obvious from the type name: asMaps() for a table with a header row, asLists() for one without, asMap() for the two-column case, then cell(), row(), column(), height(), width(), isEmpty() and transpose().

Both sidebars say plainly that TableNode and PyStringNode still work and are not deprecated, so nobody reads this as a migration they have to do.

Two things I checked rather than assumed: the version is 3.33, since 3.32.0 is the latest release and the feature is merged on 3.x; and I dropped two :ref: links I had first written to a TableNode and a PyStringNode section, because no such anchors exist and they would have broken the build. The class names are written out instead.

Built locally with docker compose run --rm read-the-docs-builder build: build succeeded, and the rendered page carries the new sections.

The snippet generation half of the follow-up is Behat/Behat#1878.

[acoulton]

Brilliant, thanks @Amoifr