templater: extract type conversion from evalfuncarg() Needed by the subsequent patches.

templater: drop bool support from evalastype() Future patches will split evalastype() into two functions, evalrawexp() and unwrapastype(), so we can catch the exception of type conversion. # evaluating function may bubble up inner ParseError thing = evalrawexp(context, mapping, arg) try: return unwrapastype(context, thing) except ParseError: # add hint and reraise However, evalboolean() can't be factored out in this way since it has to process boolean-like symbols as non keyword. Fortunately, it's unlikely that we'll need a general type converter supporting bool, so this patch drops it from the table.