GString.opBinaryRight

auto t1 = typeof(this)("Test ");
auto t2 = t1 ~ "A";
assert(t2.rawString == "Test A");
auto t3 = t1 ~ "B"w;
assert(t3.rawString == "Test B");
auto t4 = t1 ~ "C"d;
assert(t4.rawString == "Test C");
auto t5 = "D"w ~ t1;
assert(t5.rawString == "DTest ");