Make CFX_WideString::FromUTF8() take a CFX_ByteStringC argument.

Methods that take string arguments and do not persist them should
take *StringC types as argument rather than discrete ptr/len args.

Avoids a number of implicit casts from CFX_ByteString to char*.

BUG=

Review URL: https://codereview.chromium.org/1861183002
diff --git a/fpdfsdk/javascript/JS_Define.h b/fpdfsdk/javascript/JS_Define.h
index 4e158fd..c787259 100644
--- a/fpdfsdk/javascript/JS_Define.h
+++ b/fpdfsdk/javascript/JS_Define.h
@@ -354,8 +354,8 @@
                         const v8::PropertyCallbackInfo<v8::Integer>& info) {
   v8::Isolate* isolate = info.GetIsolate();
   v8::String::Utf8Value utf8_value(property);
-  CFX_WideString propname =
-      CFX_WideString::FromUTF8(*utf8_value, utf8_value.length());
+  CFX_WideString propname = CFX_WideString::FromUTF8(
+      CFX_ByteStringC(*utf8_value, utf8_value.length()));
   CJS_Object* pJSObj =
       reinterpret_cast<CJS_Object*>(FXJS_GetPrivate(isolate, info.Holder()));
   Alt* pObj = reinterpret_cast<Alt*>(pJSObj->GetEmbedObject());
@@ -377,8 +377,8 @@
       reinterpret_cast<CJS_Object*>(FXJS_GetPrivate(isolate, info.Holder()));
   Alt* pObj = reinterpret_cast<Alt*>(pJSObj->GetEmbedObject());
   v8::String::Utf8Value utf8_value(property);
-  CFX_WideString propname =
-      CFX_WideString::FromUTF8(*utf8_value, utf8_value.length());
+  CFX_WideString propname = CFX_WideString::FromUTF8(
+      CFX_ByteStringC(*utf8_value, utf8_value.length()));
   CFX_WideString sError;
   CJS_PropValue value(pRuntime);
   value.StartGetting();
@@ -404,8 +404,8 @@
       reinterpret_cast<CJS_Object*>(FXJS_GetPrivate(isolate, info.Holder()));
   Alt* pObj = reinterpret_cast<Alt*>(pJSObj->GetEmbedObject());
   v8::String::Utf8Value utf8_value(property);
-  CFX_WideString propname =
-      CFX_WideString::FromUTF8(*utf8_value, utf8_value.length());
+  CFX_WideString propname = CFX_WideString::FromUTF8(
+      CFX_ByteStringC(*utf8_value, utf8_value.length()));
   CFX_WideString sError;
   CJS_PropValue PropValue(CJS_Value(pRuntime, value, CJS_Value::VT_unknown));
   PropValue.StartSetting();
@@ -427,8 +427,8 @@
       reinterpret_cast<CJS_Object*>(FXJS_GetPrivate(isolate, info.Holder()));
   Alt* pObj = reinterpret_cast<Alt*>(pJSObj->GetEmbedObject());
   v8::String::Utf8Value utf8_value(property);
-  CFX_WideString propname =
-      CFX_WideString::FromUTF8(*utf8_value, utf8_value.length());
+  CFX_WideString propname = CFX_WideString::FromUTF8(
+      CFX_ByteStringC(*utf8_value, utf8_value.length()));
   CFX_WideString sError;
   if (!pObj->DelProperty(pContext, propname.c_str(), sError)) {
     CFX_ByteString cbName;