Replace some uses of OUStringChar with string literals

(At least MSVC++ 14.14, aka Visual Studio 2017 version 15.7, apparently requires
`"\xDFFF"` to be written with a `u` prefix in the concatenated string literal

  u"\xD800" "\U000103FF" "\xDFFF" "A"

to avoid "error C2022: '57343': too big for character", so prefix all the
individual string literals in such concatenations, even if that should be
redundant.)

Change-Id: Ief69e6c7ae71fe2c4c9c56c38fab0bc782ceb82c
Reviewed-on: https://gerrit.libreoffice.org/81142
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>

sal/qa/rtl/uri/rtl_testuri.cxx

@@ -181,11 +181,10 @@ void Test::test_Uri() {
 
     // Check surrogate handling:
 
-    aText1 = OUStringChar(u'\xD800') + // %ED%A0%80
-             OUStringChar(u'\xD800') + // %F0%90%8F%BF
-             OUStringChar(u'\xDFFF') +
-             OUStringChar(u'\xDFFF') + // %ED%BF%BF
-             "A"; // A
+    aText1 = u"\xD800" // %ED%A0%80
+             u"\U000103FF" // 0xD800,0xDFFF -> %F0%90%8F%BF
+             u"\xDFFF" // %ED%BF%BF
+             u"A"; // A
     aText2 = "%ED%A0%80" "%F0%90%8F%BF" "%ED%BF%BF" "A";
     CPPUNIT_ASSERT_EQUAL_MESSAGE(
         "failure 11",
@@ -207,11 +206,7 @@ void Test::test_Uri() {
             RTL_TEXTENCODING_UTF8));
 
     aText1 = "%ed%a0%80" "%f0%90%8f%bf" "%ed%bf%bf" "A";
-    aText2 = "%ED%A0%80" +
-              OUStringChar(u'\xD800') +
-              OUStringChar(u'\xDFFF') +
-              "%ED%BF%BF"
-              "A";
+    aText2 = u"%ED%A0%80" u"\U000103FF" u"%ED%BF%BF" u"A";
     CPPUNIT_ASSERT_EQUAL_MESSAGE(
         "failure 14",
         aText2,
@@ -247,8 +242,7 @@ void Test::test_Uri() {
     // Check IURI handling:
 
     aText1 = "%30%C3%BF";
-    aText2 = "%30" +
-             OUStringChar(u'\x00FF');
+    aText2 = u"%30\u00FF";
     CPPUNIT_ASSERT_EQUAL_MESSAGE(
         "failure 18",
         aText2,