add fixtures for hermes and react-native sourcemaps

Author: Swatinem

.gitignore

@@ -1,2 +1,3 @@
+.DS_Store
 target
 Cargo.lock

tests/fixtures/hermes/README.md

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+The sourcemap here was generated like this:
+
+```sh
+    $ hermes -O -emit-binary -output-source-map -out=output input.js
+```
+
+When running the bytecode, we get the following stacktrace:
+
+```
+Error: lets throw!
+    at foo (address at unknown:1:57)
+    at global (address at unknown:1:27)
+```

tests/fixtures/hermes/input.js

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+foo();
+
+function foo() {
+    throw new Error("lets throw!");
+}

tests/fixtures/hermes/output.map

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+The sourcemap here was generated like this:
+
+Basically this is the same that the `react-native` gradle file does, see:
+https://github.com/facebook/react-native/blob/4185a45be40e014d5e6315c70de00fe5f76c726a/react.gradle#L156-L204
+
+```sh
+    $ npx react-native bundle --platform android --entry-file input.js --bundle-output intermediate.js --sourcemap-output intermediate.js.map
+    $ hermes -O -emit-binary -output-source-map -out=intermediate2 intermediate.js
+    $ node react-native/scripts/compose-source-maps.js intermediate.js.map intermediate2.js.map -o output.map
+```
+
+When running the bytecode, we will get the following stacktrace
+(probably a bit different when done in react-native properly):
+
+```
+Error: lets throw!
+    at foo (address at unknown:1:11939)
+    at anonymous (address at unknown:1:11857)
+    at loadModuleImplementation (address at unknown:1:2608)
+    at guardedLoadModule (address at unknown:1:1973)
+    at metroRequire (address at unknown:1:1494)
+    at global (address at unknown:1:508)
+```

tests/fixtures/react-native-hermes/README.md

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+import { foo } from "./module.js"
+
+foo();

tests/fixtures/react-native-hermes/input.js

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+export function foo() {
+    throw new Error("lets throw!");
+}