libyaml refuses to skip a tab in the inter-token whitespace whenever a
simple key is allowed, so a tab used as valid separation (after a '-',
'?', or ':' indicator, or before a flow collection) is reported as a
character that cannot start a token. But a tab is legal in-line
separation; it is only illegal as indentation.
The scanner now skips tabs in scan_to_next_token and records in
tabbedSeparation whether one preceded the pending token. A block entry,
an explicit key, or an implicit mapping key promoted by ':' is rejected
when reached through a tab (there the tab would be indentation), while a
scalar value or a flow collection is accepted. Tab-indented keys and
'-\t-' nested entries still reject.
Surpasses libyaml on 6BCT, 6CA3, A2M4, DK95/00, Q5MG, Y79Y/010.
Port score 299 -> 305.
Mihaela Mihaljevic
b2d2d2f595