Evaluate committing the generate mbgl Xcode project

[julianrex]

If we commit the generated mbgl Xcode project (that's created by make iproj), we should be able to better support building from source without requiring tool dependencies (e.g. cmake).

We need to spend some time investigating this, as it will unlock supporting building with Carthage's --no-use-binaries option.

See also #109

[julianrex]

Things to consider:

• Converting absolute to relative paths
• Does this lock us to a particular Xcode version? Is that a problem?

[julianrex]

cc @nishant-karajgikar

[1ec5]

Does this lock us to a particular Xcode version? Is that a problem?

No, Xcode is very lenient about project format versions. Xcode 11 can still open projects generated in Xcode 3.2. If anything, building from source makes us more flexible in terms of Xcode versions.

[knov]

cc @misterkerry

[julianrex]

This is no longer valid.