compiler: record final type for numeric expressions

compiler: record final type for numeric expressions

    Inlinable function bodies are generated after the determine_types pass,
    so we know the type for all constants.  Rather than try to determine
    it again when inlining, record the type in the export data, using a
    $convert expression.  Reduce the number of explicit $convert
    expressions by recording a type context with the expected type in
    cases where that type is known.

    Reviewed-on: https://go-review.googlesource.com/c/150071

From-SVN: r266534