Foundation Classes - Enhance TCollection_ExtendedString with std::u16string_view support (#1009)

- Added constructor and assignment operator for std::u16string_view.
- Implemented conversion operator to std::u16string_view.
- Introduced methods to append std::u16string_view.
- Added Copy and assignment operator overloads for char16_t pointers.
- Fixed variable name inconsistencies (myLength vs mylength).
- Added new string manipulation methods: LeftAdjust, RightAdjust, LeftJustify, RightJustify, Center, Capitalize, Prepend, FirstLocationInSet, FirstLocationNotInSet, IntegerValue, IsIntegerValue, RealValue, IsRealValue, IsSameString.

src/ApplicationFramework/TKXmlL/XmlMDataStd/XmlMDataStd_ExtStringArrayDriver.cxx

@@ -319,7 +319,7 @@ void XmlMDataStd_ExtStringArrayDriver::Paste(const occ::handle<TDF_Attribute>& t
     }
     if (xstr.SearchFromEnd(c) == isym - 1)
       isym--; // replace the last separator by '\0'
-    xstr.SetValue(isym, '\0');
+    xstr.SetValue(isym, u'\0');
 #ifdef _DEBUG
     TCollection_AsciiString cstr(xstr, '?'); // deb
 #endif