Fallback to standard Bundle access when running outside JNI environment

[marcprux]

When testing a Skip Fuse module that tries to access Bundle.module via skip android test, the following crash would happen:

SwiftJNI/SwiftJNI.swift:72: Precondition failed: JNI.jni was unset
Current stack trace:
0    libswiftCore.so                    0x00000074229f0304 swift_reportError + 44
1    libswiftCore.so                    0x0000007422a8a134 _swift_stdlib_reportFatalErrorInFile + 128
2    libswiftCore.so                    0x0000007422743980 <unavailable> + 1841536
3    libswiftCore.so                    0x000000742289c364 _assertionFailure(_:_:file:line:flags:) + 160
4    libSwiftJNI.so                     0x000000741c90b880 jniContext<A>(_:) + 312
5    libSkipAndroidBridge.so            0x00000074359aba7c static BundleAccess.main.getter + 64
6    libSkipAndroidBridge.so            0x000000743599f160 <unavailable> + 774496
7    libswiftCore.so                    0x0000007422a8b8c8 <unavailable> + 5281992
8    libSkipAndroidBridge.so            0x000000743599f11c <unavailable> + 774428
9    libSkipAndroidBridge.so            0x00000074359a05f4 static AndroidBundle.main.getter + 24
10   SkipLocalizationJNIReproPackageTests.xctest 0x000000623ec4eb68 <unavailable> + 76648
11   SkipLocalizationJNIReproPackageTests.xctest 0x000000623ec4ef04 <unavailable> + 77572
12   libswiftCore.so                    0x0000007422a8b8c8 <unavailable> + 5281992
13   SkipLocalizationJNIReproPackageTests.xctest 0x000000623ec4ef30 <unavailable> + 77616
14   SkipLocalizationJNIReproPackageTests.xctest 0x000000623ec4eab8 <unavailable> + 76472
15   SkipLocalizationJNIReproPackageTests.xctest 0x000000623ec7a220 <unavailable> + 254496
16   SkipLocalizationJNIReproPackageTests.xctest 0x000000623ec79b48 <unavailable> + 252744
17   libswift_Concurrency.so            0x000000743058ed34 <unavailable> + 552244
18   libswift_Concurrency.so            0x000000743058f978 swift_job_run + 164
19   libdispatch.so                     0x000000741c68c448 <unavailable> + 226376
20   libdispatch.so                     0x000000741c68c28c <unavailable> + 225932
21   libdispatch.so                     0x000000741c6966e8 <unavailable> + 268008
22   libc.so                            0x000000742f3546ac <unavailable> + 833196
23   libc.so                            0x000000742f2f1220 <unavailable> + 426528
Trap 

Error: Error terminated(code: 1) running command: /Users/marc/Library/Android/sdk/platform-tools/adb shell cd '/data/local/tmp/swift-android/SkipLocalizationJNIRepro-8AF0F2E3-AAFA-4411-890D-8411EAC2E893/' && ./SkipLocalizationJNIReproPackageTests.xctest && ./SkipLocalizationJNIReproPackageTests.xctest --testing-library swift-testing && [ $? -eq 0 ] || [ $? -eq 69 ]

As discussed at https://skip.dev/docs/testing/, skip android test is a "bare-bones" testing tool, in that it runs the tests as a bare native Android executable, rather than bundling everything into an .apk and executing instrumented tests like skip test --android-serial=emulator-5554 does.

This is normally fine, but when the module under test incorporates Skip by using the skipstone plugin, then we generate a shim to intercept bundle access and redirect it to Skip's bridged Bundle support, which integrates with our packaging of the SwiftPM resources into the apk's assets/ folder and uses the AssetManager to retrieve these resources. None of this happens at all under the bare metal testing of skip android test, and so it doesn't work: we crash when we first try to bridge through to Skip because there is no ambient java environment in this scenario.

This PR provides a stopgap that bypasses bridging and falls back to the default Linux-style .resources/ folder handling that a non-Skip project would use.