Fix issue 12916 - index based insert

[Safety0ff]

https://issues.dlang.org/show_bug.cgi?id=12916

I have not yet reviewed the code, don't pull. It's a PR so it doesn't fall off the radar.

[DmitryOlshansky]

Going to review this and #2240 soonish (in a day or two). Stay tuned.

[Safety0ff]

Going to review this and #2240 soonish (in a day or two). Stay tuned.

Noted, I'll try to have a look at beforehand.

[DmitryOlshansky]

I took a peek and this is about unviling not-in-place insert. Looks OK, and I caught myself that I again forget that hasLength returns false for strings.

Would be nice to add a bit of Unicode symbols into string tests. Otherwise good to go.

[Safety0ff]

Would be nice to add a bit of Unicode symbols into string tests.

Ok, I'll use the tests for insertInPlace as a guide for unicode testing.

[Safety0ff]

I started looking into the tests, but I think that it should have a similar interface to insertInPlace to avoid asymmetry of API, so this is on my back burner. I'll focus on #2240 , it's API already matches the other replace functions.

[Safety0ff]

Closing for the time being.