Add support for installing via Bazel

[NickEntin]

ERROR: /private/var/tmp/_bazel_runner/e29028f8b05bab84afa05bb51b12f3f3/external/ios_snapshot_test_case/BUILD.bazel:21:14: Compiling Swift module @ios_snapshot_test_case//:iOSSnapshotTestCase failed: (Exit 1): worker failed: error executing command (from target @ios_snapshot_test_case//:iOSSnapshotTestCase) bazel-out/darwin-opt-exec-2B5CBBC6-ST-4f4ca27b179b/bin/external/build_bazel_rules_swift/tools/worker/worker swiftc ... (remaining 1 argument skipped)
error: emit-module command failed with exit code 1 (use -v to see invocation)
external/ios_snapshot_test_case/src/iOSSnapshotTestCase/SwiftSupport.swift:11:8: error: no such module 'XCTest'
import XCTest
       ^
<module-includes>:1:9: note: in file included from <module-includes>:1:
#import "../../../../../external/ios_snapshot_test_case/src/iOSSnapshotTestCaseCore/Public/FBSnapshotTestCase.h"
        ^
external/ios_snapshot_test_case/src/iOSSnapshotTestCase/SwiftSupport.swift:11:8: error: no such module 'XCTest'
import XCTest
       ^
<module-includes>:1:9: note: in file included from <module-includes>:1:
#import "../../../../../external/ios_snapshot_test_case/src/iOSSnapshotTestCaseCore/Public/FBSnapshotTestCase.h"
        ^

🤔

[NickEntin]

• [ ] Fix the iOSSnapshotTestCase extension not building due to inability to resolve XCTest
• [ ] Add rule for SnapshotTesting extension (need to convert from SPM)