ArrowFunction carries the surrounding In grammar parameter into its
ConciseBody. The parser recognized arrows in for-loop init expressions,
but parsed expression bodies with In always enabled, so
`for (x => 0 in 1;;)` was accepted as a normal for loop.
Thread the existing forbidden-token state through arrow parsing so the
body leaves `in` for the for-head parser. That parser then rejects the
arrow as an invalid for-in left-hand side. Add coverage in the for-loop
no-In syntax test.
SingleNameBinding default initializers use NamedEvaluation when the
argument value is undefined and the initializer is an anonymous function
or class definition.
Set the pending inferred name while evaluating default initializers for
identifier parameters, and add coverage for function, generator, async,
arrow, and class expressions.
