Everywhere: Convert ByteBuffer factory methods from Optional -> ErrorOr

Apologies for the enormous commit, but I don't see a way to split this
up nicely. In the vast majority of cases it's a simple change. A few
extra places can use TRY instead of manual error checking though. :^)

Tests/Kernel/stress-writeread.cpp

@@ -85,7 +85,7 @@ int main(int argc, char** argv)
     args_parser.parse(argc, argv);
 
     auto buffer_result = AK::ByteBuffer::create_zeroed(block_size);
-    if (!buffer_result.has_value()) {
+    if (buffer_result.is_error()) {
         warnln("Failed to allocate a buffer of {} bytes", block_size);
         return EXIT_FAILURE;
     }