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. :^)

Userland/DevTools/UserspaceEmulator/SoftMMU.cpp

@@ -321,7 +321,7 @@ void SoftMMU::copy_from_vm(void* destination, const FlatPtr source, size_t size)
 
 ByteBuffer SoftMMU::copy_buffer_from_vm(const FlatPtr source, size_t size)
 {
-    auto buffer = ByteBuffer::create_uninitialized(size).release_value(); // FIXME: Handle possible OOM situation.
+    auto buffer = ByteBuffer::create_uninitialized(size).release_value_but_fixme_should_propagate_errors(); // FIXME: Handle possible OOM situation.
     copy_from_vm(buffer.data(), source, size);
     return buffer;
 }