add range support to std.string.stripLeft

[WalterBright]

unit test coverage 100%

[JakobOvrum]

std.algorithm.mutation already has generic strip, stripLeft and stripRight. The string versions that use isWhite should probably be composed in terms of the generic ones?

[WalterBright]

Unfortunately, the generic strip does not decode ranges of char or wchar:

import std.stdio;
import std.algorithm;
import std.utf;
import std.array;

void main() {
    assert("ëëêéüŗōpéêëë".strip('ë') == "êéüŗōpéê"); // works
    assert("ëëêéüŗōpéêëë".byCodeUnit.strip('ë').array == "êéüŗōpéê"); // fails
}

[JesseKPhillips]

Instead of calling .array, you should be able to use .equal to verify equality and you won't have an allocation.

[WalterBright]

Being a test case, the allocation doesn't matter.

[JakobOvrum]

While I would prefer changing std.algorithm's strip functions and deferring to those, the interface would be the same and this is a tiny patch, so LGTM.

[JakobOvrum]

Auto-merge toggled on

[aG0aep6G]

This introduced a regression: https://issues.dlang.org/show_bug.cgi?id=14827