Fix cppia JIT "Bad move target" on untyped register moves

[MeguminBOT]

Any binary subtraction inside a ternary that is converted to String or object triggers it.
Multiplication, division, unary minus and addition are unaffected, as is hoisting the subtraction into a local first.

CppiaCompiler::convert moved between two registers without giving either a type in three places.
move() decides what to emit from getCommonType(), and getCommonType(jtAny, jtAny) returns jtAny, which the
switch answers with setError("Bad move target").

All three sites are guarded by inSrc.uses(SLJIT_R1) or inSrc==sJitTemp1, so they are only reached when the source value happens to live in R1.
OpAdd::genCode leaves its int result in sJitTemp0 and misses the guard, while OpSub::genCode uses sJitTemp1 and hits it, which is why addition compiles and subtraction does not.

Reproducable steps

class Repro {
    static function f(a:Int, b:Int, flag:Bool):String {
        return "x" + (flag ? 0 : a - b);
    }
    public static function main() Sys.println(f(5, 3, false));
}

Run

haxe -main Repro -cppia repro.cppia
haxe -main cpp.cppia.Host -D scriptable -dce no -cpp host
host/Host.exe -jit repro.cppia    Error : Bad move target
host/Host.exe      repro.cppia    x2