A tab is separation white space in YAML, so it follows the `:` mapping-value
indicator exactly as a space does. isMappingValueBoundary (flow) and
isBlockMappingValueBoundary (block) accepted only a space, line break, comma,
or closing bracket, so `foo:\tbar` folded into the plain scalar `foo:\tbar`
instead of the mapping `{foo: bar}`.
Accept a tab in both. A `:` with no following white space (`foo:bar`) is still
plain scalar content, and the symmetric counterpart for a tab after a leading
indicator landed in the previous change.
Raises yaml-test-suite parse-level to 300/333 (90.1%) with the should-error
rejection rate unchanged. 433 tests pass.
Mihaela M
738408d458