Make CFX_WideString::FromLocal() take a CFX_ByteStringC arg

It doesn't persist the string beyond the duration of the
call, hence it should take the *StringC variant. Doing so
avoids some allocs by changing to the *StringC ctor in a few
places, at the cost of some explicit .ToByteStringC() calls
(which are cheap).

Review URL: https://codereview.chromium.org/1862953004
diff --git a/fpdfsdk/javascript/PublicMethods.cpp b/fpdfsdk/javascript/PublicMethods.cpp
index 308163d..d5b961d 100644
--- a/fpdfsdk/javascript/PublicMethods.cpp
+++ b/fpdfsdk/javascript/PublicMethods.cpp
@@ -837,7 +837,7 @@
   }
 
   // for processing currency string
-  Value = CFX_WideString::FromLocal(strValue);
+  Value = CFX_WideString::FromLocal(strValue.AsByteStringC());
   std::wstring strValue2 = Value.c_str();
 
   if (bCurrencyPrepend)
@@ -1120,7 +1120,7 @@
   if (iNegative)
     strValue = "-" + strValue;
   strValue += "%";
-  Value = CFX_WideString::FromLocal(strValue);
+  Value = CFX_WideString::FromLocal(strValue.AsByteStringC());
 #endif
   return TRUE;
 }