Compute some ImmutableScriptFlags for functions

[arai-a]

• FunctionHasThisBinding
  • if this is used
• HasInnerFunctions
  • if there's inner function
• NeedsFunctionEnvironmentObjects
  • if a binding in function scope is closed over, or
  • has extensible scope (has direct eval in non-strict), or
  • is generator, or
  • is async
• FunctionHasExtraBodyVarScope
• ShouldDeclareArguments
• ArgumentsHasVarBinding
• AlwaysNeedsArgsObj
• HasMappedArgsObj