fix: Allow EnableEmbeddedAsarIntegrityValidation when multiple asars are present in app (#124)

- When an application uses multiple asars (`webapp.asar`, `anything.asar`, etc.), `EnableEmbeddedAsarIntegrityValidation` fuse breaks the application due to not all asars having integrity generated for them. Fixes: #116
- **Also fixes bug** to correctly test `makeUniversalApp no asar mode should shim two different app folders`, (it was not having an asar integrity generated for the shimmed asar)

Functionality added:
- Moves all asar integrity generation to **after** all app assets have been merged/shimmed/copied. This allows other asars that were provided to also be scanned and have asar integrity generated for them.
- Extracted common Integrity logic to a single file `integrity.ts`
- Adds unit test for multi-asar apps

test/util.ts

@@ -14,6 +14,7 @@ export const VERIFY_APP_TIMEOUT = 80 * 1000;
 
 export const asarsDir = path.resolve(__dirname, 'fixtures', 'asars');
 export const appsDir = path.resolve(__dirname, 'fixtures', 'apps');
+export const appsOutPath = path.resolve(appsDir, 'out');
 
 export const verifyApp = async (appPath: string) => {
   await ensureUniversal(appPath);