add failing tests for default function export

The first one seems to be a bug.

The second two are to do with allowing the default token, so perhaps these are not as urgent and could be omitted.


Implementation wise this is easy. Parse it as a FunctionExpression and if it has a name reparse it as a FunctionDefinition. In this case FunctionExpression can act as the cover grammar
.
See CoverParenthesizedExpressionAndArrowParameterList and CoverInitializedName in the spec for other use cases of cover grammars.