Make analyzer skip the embedded target -> host compatibility check for hosts not defined in the Podfile

Improved clarity of title for #5726 summary entry.

Capitalized “Messages” to make clear that it is a product name reference (Mac/iOS Messages.app), and added a verb to clarify that the fix pertains to the end use of CocoaPods as opposed to its integration with something else.

Verify embedded target platform/swift matches its host

Use the project-level swift version when not defined at the target-level

Set ALWAYS_EMBED_SWIFT_STANDARD_LIBRARIES when appropriate

Improved messages when missing host targets in the Podfile. Improved framework-only dev support.

- Add support for framework-only development

Added support for message extensions embedded in messages applications

Make embedded target host verification consider all known user projects

Corrected duplicate 'by grouping' in comment.