[build] Package bcsymbolmap files; cleanup packaging script

[friedbunny]

.bcsymbolmap files are text files with a list of symbols available in our framework, used to map recompiled bitcode to named symbols for crash reporting. These files are generated in the build process, one per device architecture, and share UUIDs with those slices/dSYMs.

These bcsymbolmap files can be included during the app archiving process and uploaded to Apple.

• Carthage does this automatically. (Copy bcsymbolmap files when building Carthage/Carthage#853)
• CocoaPods does not. (It’s only just now getting proper dSYM support. 😑)
• Our standalone-install strip-framework.sh already supports this. (Copy bcsymbolmap files to build products folder when archiving realm/realm-swift#2759)

08b963e packages these files alongside our dynamic framework. When uploaded with an app archive, this should theoretically help eliminate the pesky __hidden symbols issue (#8463).

Notes

• Documentation on bcsymbolmap is rare and mostly anecdotal, as one expects of an Apple build process detail.
• There are rumors that Xcode 9 will stop producing them.
• bcsymbolmaps are only generated for dynamic frameworks, similar to dSYMs.
• Many framework vendors don’t bother bundling these, but Realm and PSPDFKit do.
• These files are large: 2.7 MB uncompressed, ~18K lines — see this example.
• Like most debug ephemera, they aren’t shipped in the final end-user app.

Also did some more Fabric cleanup

612a1e8 follows up on #9264 and removes the Fabric-specific static framework + bundle mode, first introduced in #4232, later updated in #4783.

/cc @1ec5 @boundsj @fabian-guerra

[friedbunny]

Looking more closely at strip-frameworks.sh, it assumes the bcsymbolmap files are in the framework folder itself, not just packaged alongside. We can change this PR to put them inside the framework, but I want to reconfirm that these files aren’t shipped with apps (or, we should find a foolproof way to delete them).

Update: they’ll be shipped if you don’t move/delete them from the framework.

[1ec5]

Worth a changelog entry?

[friedbunny]

Turns out that Carthage won’t copy in bcsymbolmaps from precompiled binaries (only frameworks it builds itself), so that’s a bummer. Still, including these files in the distribution has no downside and is potentially valuable, if the developer chooses to take advantage of them and/or if package manager support improves.

Carthage/Carthage#684 and CocoaPods/CocoaPods#6536 show the way forward, if someone wanted to implement support.