Resolve issue where ConstString can lose internal string representation due to not owning it.

This sadly meant most constexpr constructors had to be removed, as it needs to copy the string.

tests/ConstStringTests.cpp

@@ -42,5 +42,23 @@ TEST_CASE("Use case insensitive const string in switch case", "[Utilities]") {
     }
 }
 
+__attribute__((optnone))
+static Arbutils::CaseInsensitiveConstString TestCreateConstString(){
+    char originalVal [6];
+    originalVal[0] = 'f';
+    originalVal[1] = 'o';
+    originalVal[2] = 'o';
+    originalVal[3] = 'b';
+    originalVal[4] = 'a';
+    originalVal[5] = 'r';
+    return Arbutils::CaseInsensitiveConstString(originalVal);
+}
+
+TEST_CASE("Out of scope char* doesn't lose reference", "[Utilities]") {
+    Arbutils::CaseInsensitiveConstString val = TestCreateConstString();
+    INFO(val.c_str());
+    REQUIRE(strcmp(val.c_str(), "foobar") == 0);
+}
+
 
 #endif