scripts/qapi: Move doc-comment whitespace stripping to doc.py

scripts/qapi: Move doc-comment whitespace stripping to doc.py

As we accumulate lines from doc comments when parsing the JSON, the
QAPIDoc class generally strips leading and trailing whitespace using
line.strip() when it calls _append_freeform().  This is fine for
Texinfo, but for rST leading whitespace is significant.  We'd like to
move to having the text in doc comments be rST format rather than a
custom syntax, so move the removal of leading whitespace from the
QAPIDoc class to the texinfo-specific processing code in
texi_format() in qapi/doc.py.

(Trailing whitespace will always be stripped by the rstrip() in
Section::append regardless.)

In a followup commit we will make the whitespace in the lines of doc
comment sections more consistently follow the input source.

There is no change to the generated .texi files before and after this
commit.

Because the qapi-schema test checks the exact values of the
documentation comments against a reference, we need to update that
reference to match the new whitespace.  In the first four places this
is now correctly checking that we did put in the amount of whitespace
to pass a rST-formatted list to the backend; in the last two places
the extra whitespace is 'wrong' and will go away again in the
following commit.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Message-Id: <20200925162316.21205-5-peter.maydell@linaro.org>
Signed-off-by: Markus Armbruster <armbru@redhat.com>