[Issue 19308] Optimize std.string.stripLeft

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=19308

--- Comment #2 from github-bugzilla at puremagic.com ---
Commit pushed to master at https://github.com/dlang/phobos

https://github.com/dlang/phobos/commit/2e6c538dc69b74125cfd7f39376b0d9289565728
Fix issue 19308 - optimize stripLeft

Add ASCII fast path to stripLeft & avoid redundant decoding.

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