A property written inline before a block mapping's first key (`&a key: v`) was
attached to the whole mapping, so an anchor registered only when the mapping
ended, too late for an alias inside one of the mapping's values to resolve.
The YAML grammar requires a block collection's own properties to be followed by
a line break (`s-l+block-collection`), so a property on the first key's line
belongs to the key, not the collection. The mapping now keeps only a property
written on its own line above the first key; an inline one is threaded back to
the first pair, where the key parses it and an anchor registers with the key.
Fixes yaml-test-suite 2SXE (`&a:` and `&a` are distinct anchors, since a name
includes a trailing `:`) and HMQ5 (a key carrying both a tag and an anchor).
Raises parse-level conformance to 308/333 (92.5%) and value-level to 201/201
(100.0%), with the should-error rate unchanged.
Mihaela M
c858339307