Fix return scope -> return ref in as_array()

[dkorpel]

return scope was added to core.stdcpp.string.basic_string.as_array in #3754 for version(CppRuntime_Microsoft) and in #3757 for version(CppRuntime_Clang), because theinout -> return ref implication was removed and return/scope inference was not good at dealing with the ambiguity of return ref and return scope.

Now with dlang/dmd#13860, it turns out that for version(CppRuntime_Clang) return scope is incorrect, because it has a small buffer optimization, so it should be return ref. For uniformity, I made the version(CppRuntime_Microsoft) return ref as well.

[dlang-bot]

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