Cocoapods Build From Source

[neelmistry94]

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Fixes: < Link to related issues that will be fixed by this pull request, if they exist >

Pull request checklist:

• Briefly describe the changes in this PR.
• Apply changelog label ('breaking change', 'bug 🪲', 'build', 'docs', 'feature 🍏', 'performance ⚡', 'testing 💯') or use the label 'skip changelog'
• Add an entry inside this element for inclusion in the mapbox-maps-ios changelog: <changelog>Consumption of MapboxMaps via Cocoapods will now build from source</changelog>.

Summary of changes

Updates the podspec to use a build from source approach. It also defaulting to updating source builds for MME and Turf.

In order to test

1. Create a new Xcode project
2. In the command line, navigate to the root of your new tester app, and then type pod init. This will create a Podfile for you.
3. Open your Podfile, and under your app target, add this line pod 'MapboxMaps', :git => 'https://github.com/mapbox/mapbox-maps-ios.git', :branch => 'nm/pods_build_from_source'
4. In the command line, type pod install --repo-update to install this as a dependency
5. Open your project.xcworkspace and then try building a map