* Introduce "_ptr" variants of ZIR try instruction to disallow constructs
   such as `try` on a pointer value instead of an error union value.
 * Disable the "_inline" variants of the ZIR try instruction for now because
   we are out of ZIR tags. I will free up some space in an independent commit.
 * AstGen: fix tryExpr calling rvalue() on ResultLoc.ref