Provide a public method to get StringRef's underlying pointer

This allows reducing the amount of friends needed for its interface
and some extra tricks later.

The bad part is that the pointer can become invalidated via
calls to other StringRef's public methods, but c'est la vie.

projects/SelfTest/Baselines/compact.sw.approved.txt

@@ -637,11 +637,11 @@ String.tests.cpp:<line number>: passed: std::strcmp( ss.c_str(), "hello" ) == 0
 String.tests.cpp:<line number>: passed: ss == "hello" for: hello == "hello"
 String.tests.cpp:<line number>: passed: isSubstring( ss ) for: true
 String.tests.cpp:<line number>: passed: isOwned( ss ) == false for: false == false
-String.tests.cpp:<line number>: passed: rawChars == data( s ) for: "hello world!" == "hello world!"
+String.tests.cpp:<line number>: passed: rawChars == s.currentData() for: "hello world!" == "hello world!"
 String.tests.cpp:<line number>: passed: ss.c_str() != rawChars for: "hello" != "hello world!"
 String.tests.cpp:<line number>: passed: isSubstring( ss ) == false for: false == false
 String.tests.cpp:<line number>: passed: isOwned( ss ) for: true
-String.tests.cpp:<line number>: passed: data( ss ) != data( s ) for: "hello" != "hello world!"
+String.tests.cpp:<line number>: passed: ss.currentData() != s.currentData() for: "hello" != "hello world!"
 String.tests.cpp:<line number>: passed: ss.size() == 6 for: 6 == 6
 String.tests.cpp:<line number>: passed: std::strcmp( ss.c_str(), "world!" ) == 0 for: 0 == 0
 String.tests.cpp:<line number>: passed: s.c_str() == s2.c_str() for: "hello world!" == "hello world!"

projects/SelfTest/Baselines/console.sw.approved.txt

@@ -5076,7 +5076,7 @@ with expansion:
 
 String.tests.cpp:<line number>:
 PASSED:
-  REQUIRE( rawChars == data( s ) )
+  REQUIRE( rawChars == s.currentData() )
 with expansion:
   "hello world!" == "hello world!"
 
@@ -5100,7 +5100,7 @@ with expansion:
 
 String.tests.cpp:<line number>:
 PASSED:
-  REQUIRE( data( ss ) != data( s ) )
+  REQUIRE( ss.currentData() != s.currentData() )
 with expansion:
   "hello" != "hello world!"
 

projects/SelfTest/Baselines/xml.sw.approved.txt

@@ -5808,7 +5808,7 @@ Message from section two
           </Expression>
           <Expression success="true" type="REQUIRE" filename="projects/<exe-name>/IntrospectiveTests/String.tests.cpp" >
             <Original>
-              rawChars == data( s )
+              rawChars == s.currentData()
             </Original>
             <Expanded>
               "hello world!" == "hello world!"
@@ -5840,7 +5840,7 @@ Message from section two
           </Expression>
           <Expression success="true" type="REQUIRE" filename="projects/<exe-name>/IntrospectiveTests/String.tests.cpp" >
             <Original>
-              data( ss ) != data( s )
+              ss.currentData() != s.currentData()
             </Original>
             <Expanded>
               "hello" != "hello world!"

projects/SelfTest/IntrospectiveTests/String.tests.cpp

@@ -14,9 +14,6 @@ namespace Catch {
         static auto isSubstring( StringRef const& stringRef ) -> bool {
             return stringRef.isSubstring();
         }
-        static auto data( StringRef const& stringRef ) -> char const* {
-            return stringRef.data();
-        }
     };
 
     auto isOwned( StringRef const& stringRef ) -> bool {
@@ -25,14 +22,11 @@ namespace Catch {
     auto isSubstring( StringRef const& stringRef ) -> bool {
         return StringRefTestAccess::isSubstring( stringRef );
     }
-    auto data( StringRef const& stringRef ) -> char const* {
-        return StringRefTestAccess::data( stringRef );
-    }
 } // namespace Catch2
 
 namespace Catch {
     inline auto toString( Catch::StringRef const& stringRef ) -> std::string {
-        return std::string( data( stringRef ), stringRef.size() );
+        return std::string( stringRef.currentData(), stringRef.size() );
     }
 } // namespace Catch
 
@@ -53,7 +47,7 @@ TEST_CASE( "StringRef", "[Strings][StringRef]" ) {
         REQUIRE( s.size() == 5 );
         REQUIRE( isSubstring( s ) == false );
 
-        auto rawChars = data( s );
+        auto rawChars = s.currentData();
         REQUIRE( std::strcmp( rawChars, "hello" ) == 0 );
 
         SECTION( "c_str() does not cause copy" ) {
@@ -74,7 +68,6 @@ TEST_CASE( "StringRef", "[Strings][StringRef]" ) {
 
         REQUIRE( isSubstring( original ) == false );
         REQUIRE( isOwned( original ) );
-
     }
 
 
@@ -92,14 +85,14 @@ TEST_CASE( "StringRef", "[Strings][StringRef]" ) {
             REQUIRE( isSubstring( ss ) );
             REQUIRE( isOwned( ss ) == false );
 
-            auto rawChars = data( ss );
-            REQUIRE( rawChars == data( s ) ); // same pointer value
+            auto rawChars = ss.currentData();
+            REQUIRE( rawChars == s.currentData() ); // same pointer value
             REQUIRE( ss.c_str() != rawChars );
 
             REQUIRE( isSubstring( ss ) == false );
             REQUIRE( isOwned( ss ) );
 
-            REQUIRE( data( ss ) != data( s ) ); // different pointer value
+            REQUIRE( ss.currentData() != s.currentData() ); // different pointer value
         }
 
         SECTION( "non-zero-based substring") {