Spurious static error for `char(_)` parse Tree and annotation setting

[jurgenvinju]

Describe the bug

Tree buggyFunc() {
  return char(10)[@\loc=|unknown:///|]; 
} 

This produces:

Invalid type: expected node, ADT, or concrete syntax types, found ![]

It looks like the \char-class type of the char(10) expression, which is either [\n] or ![], has not been added to the possible receivers of annotation setting [@anno=exp] yet.

I worked around this in ParseTree.rsc by "upcasting" to Tree statically, but the code would look better without that workaround.