Add config for Android API target

[bwalter]

While the compiler only needs to target one API level, the parser needs to provide version-specific diagnostics. This should probably be done with a Parser configuration as an enum, e.g.:

TargetAndroidVersion {
  Android9OrLower,
  Android10,
  Android11,
  Android12,
  AndroidT,
  All,  // unspecified (= default)
}

Exemple:

• parcelable declaration for Android10 or higher
• enum declaration for Android11 or higher
• union declaration for Android12 or higher
• nested type declaration for AndroidT or higher

Relates to bwalter/aidl-lsp#4 and bwalter/aidl-lsp#5.