WIP: new externalterm API

[bettio]

WIP, THIS PR IS STILL MEANT ONLY FOR DISCUSSION

These changes are made under both the "Apache 2.0" and the "GNU Lesser General
Public License 2.1 or later" license terms (dual license).

SPDX-License-Identifier: Apache-2.0 OR LGPL-2.1-or-later

[bettio]

1. Remove externalterm_from_const_literal. This API is used only from module_load_literal and it doesn't allow to handle out of memory in a graceful way. src/libAtomVM/opcodesswitch.h can already handle this kind of error, but we are aborting in module.c

2. We still miss support for a safe option in binary_to_term

3. Add a new API that can be more flexible

enum ExternalTermResult
{
OutOfMem,
[...]
};

enum ExternalTermOpts
{
    Copy,
    Safe
    ...
};

ExternalTermResult result externalterm_heap_from_buf(const void *buf, size_t buf_size, ExternalTermOpts opts, Heap *out_heap, term *out_term, GlobalContext *glb);

ExternalTermResult result externalterm_term_from_buf(const void *buf, size_t buf_size, ExternalTermOpts opts, term roots[], term roots_count, term *out_term, Context *ctx);

Also other opinions:
4. I think an API that allows to deal with any raw buffer containing an external term can be valuable for different use case, so we must make sure our API will support it.
5. I think that our current API with the index parameter for the binary argument might be tricky maybe.