Add inline codegen for simpler Tr codes

[DavidPH]

Currently, under ZDACS Tr unconditionally calls a function for conversion. However, this is obviously wasteful for integer->integer and probably most fixed->fixed conversions. Due to this, the higher level codegen avoids generating Tr codes for such cases, but that is in and of itself an unnecessary complication there and introduces opportunities to miss out on IR arg optimizations.