In a flow mapping the value is a flow node and may sit on any line; flow is line
insensitive. parseMappingPair gated value parsing on hasNodeOnSameLine, a
block-only rule, so a value after `:` on the next line was treated as null and
left unconsumed, failing the whole flow mapping. Thread an inFlow flag and, in
flow, parse the value as a flow node line-insensitively (only a flow terminator
leaves it null), bypassing the block-only same-line and indentation branches.
Pretty-printed JSON (a YAML 1.2 superset) relies on this. Against the JSON Schema
Test Suite corpus this fixes all 27 files that previously failed to parse
(432/432 now); the YAML test-suite (318/333, value-level 206/206) and the full
suite stay green.
