Add Realm module map generation

[matt]

Goals

Allow RealmSwift to be added as a static library via Cocoapods.

Expected Results

Realm defines modules

Actual Results

Cocoapods Error:
[!] The following Swift pods cannot yet be integrated as static libraries:

The Swift pod RealmSwift depends upon Realm, which do not define modules. To opt into those targets generating module maps (which is necessary to import them from Swift when building as static libraries), you may set use_modular_headers! globally in your Podfile, or specify :modular_headers => true for particular dependencies.

Pull Request

#6041

[leemaguire]

Given the linked issue is closed and the lack of demand for a static library I am closing this issue.