util/AllocatedString: add string_view constructor

Replaces the static Duplicate() method.

src/util/AllocatedString.hxx

@@ -65,6 +65,9 @@ public:
 	BasicAllocatedString(std::nullptr_t n) noexcept
 		:value(n) {}
 
+	explicit BasicAllocatedString(string_view src) noexcept
+		:value(Duplicate(src)) {}
+
 	BasicAllocatedString(BasicAllocatedString &&src) noexcept
 		:value(src.Steal()) {}
 
@@ -86,12 +89,6 @@ public:
 		return Donate(p);
 	}
 
-	static BasicAllocatedString Duplicate(string_view src) {
-		auto p = new value_type[src.size() + 1];
-		*std::copy_n(src.data(), src.size(), p) = SENTINEL;
-		return Donate(p);
-	}
-
 	BasicAllocatedString &operator=(BasicAllocatedString &&src) noexcept {
 		std::swap(value, src.value);
 		return *this;
@@ -138,7 +135,14 @@ public:
 	}
 
 	BasicAllocatedString Clone() const {
-		return Duplicate(*this);
+		return BasicAllocatedString(Duplicate(*this));
+	}
+
+private:
+	static pointer Duplicate(string_view src) {
+		auto p = new value_type[src.size() + 1];
+		*std::copy_n(src.data(), src.size(), p) = SENTINEL;
+		return p;
 	}
 };