Vendor all dependencies

[st3fan]

We need to start vendoring (keeping a local copy) of dependencies. For the following reasons:

• This will considerably speed up the build, since no dependencies will have to be fetched.
• It will guarantee stability since we will build with a known set of dependencies
• Security-wise it is better to vendor because we do not know for sure what we will pull in from the network

It is unclear if the current tooling supports this. Needs investigation. If not, we should submit a request in the Swift issue tracker.

┆Issue is synchronized with this Jira Task

[st3fan]

It doesn’t look like Swift currently has support for this. Needs more investigation. I think the least we should do is probably to fork the dependencies so that we have a backup copy around.

[st3fan]

It would be great to find out if this is possible with Xcode 13.