build(android): bump compileSdk to 37 and pin file_picker to beta.5

Pin file_picker to exact 12.0.0-beta.5 since beta.7's published artifact fails to compile on Android. Set compileSdk = 37 so receive_sharing_intent 1.9.0 (compiles against SDK 37) builds against a stable platform.

android/app/build.gradle.kts

@@ -17,7 +17,7 @@ if (keystorePropertiesFile.exists()) {
 
 android {
     namespace = "com.zarz.spotiflac"
-    compileSdk = flutter.compileSdkVersion
+    compileSdk = 37
     ndkVersion = flutter.ndkVersion
 
     buildFeatures {