qapi: Recognize section tags and 'Features:' only after blank line

Putting a blank line before section tags and 'Features:' is good,
existing practice.  Enforce it.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-ID: <20240216145841.2099240-12-armbru@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>

tests/qapi-schema/doc-duplicated-return.err

@@ -1 +1 @@
-doc-duplicated-return.json:7:1: duplicated 'Returns' section
+doc-duplicated-return.json:8:1: duplicated 'Returns' section

tests/qapi-schema/doc-duplicated-return.json

@@ -4,5 +4,6 @@
 # @foo:
 #
 # Returns: 0
+#
 # Returns: 1
 ##

tests/qapi-schema/doc-duplicated-since.err

@@ -1 +1 @@
-doc-duplicated-since.json:7:1: duplicated 'Since' section
+doc-duplicated-since.json:8:1: duplicated 'Since' section

tests/qapi-schema/doc-duplicated-since.json

@@ -4,5 +4,6 @@
 # @foo:
 #
 # Since: 0
+#
 # Since: 1
 ##

tests/qapi-schema/doc-good.json

@@ -154,22 +154,29 @@
 # Features:
 # @cmd-feat1: a feature
 # @cmd-feat2: another feature
+#
 # Note: @arg3 is undocumented
+#
 # Returns: @Object
+#
 # TODO: frobnicate
+#
 # Notes:
 #
 #  - Lorem ipsum dolor sit amet
 #  - Ut enim ad minim veniam
 #
 #  Duis aute irure dolor
+#
 # Example:
 #
 #  -> in
 #  <- out
+#
 # Examples:
 #  - *verbatim*
 #  - {braces}
+#
 # Since: 2.10
 ##
 { 'command': 'cmd',
@@ -180,9 +187,11 @@
 ##
 # @cmd-boxed:
 # If you're bored enough to read this, go see a video of boxed cats
+#
 # Features:
 # @cmd-feat1: a feature
 # @cmd-feat2: another feature
+#
 # Example:
 #
 #  -> in

tests/qapi-schema/doc-invalid-return.err

@@ -1 +1 @@
-doc-invalid-return.json:5: 'Returns:' is only valid for commands
+doc-invalid-return.json:6: 'Returns:' is only valid for commands

tests/qapi-schema/doc-invalid-return.json

@@ -2,6 +2,7 @@
 
 ##
 # @FOO:
+#
 # Returns: blah
 ##
 { 'event': 'FOO' }