FunctionDeclaration: Fix children type
FunctionDeclaration: Add default arguments
RedHatTransformer: Don’t use dynamic token for dec

The parser uses the ‘void’ or ‘function’ token for the declaration /
definition, but not the ‘dynamic’ token.
Add FunctionDefinition (RedHat’s MethodDefinition)
Add tests for FunctionDefinition backend conversion
RedHatTransformer: correct tokens for values

For a ValueDefinition or ValueGetterDefinition (AttributeDeclaration,
AttributeGetterDeclaration / inferredAttributeDeclaration,
typedMethodOrAttributeDeclaration) with a ‘value’ modifier, the parser
adds the ‘value’ token as the definition’s main token as well, for some
reason.