Feat/access local network 9

[fabiomartino]

Android 16 (API 37) blocks local-network addresses by default and introduces
ACCESS_LOCAL_NETWORK as a runtime permission. Without framework support,
apps using CapacitorHttp against LAN devices fail with timeouts on API 37+.

This change:

• declares android.permission.ACCESS_LOCAL_NETWORK in the core library
  manifest (merged into every app, safely ignored on older SDKs);
• adds a version-aware PermissionHelper gate (isPermissionEnforced, with
  string literal + literal API 37 constant so the compile SDK can stay
  below 37);
• reports the permission as GRANTED on SDKs below 37 and only runs the
  manifest check / DENIED caching on enforced SDKs, in both
  Bridge.validatePermissions() and Bridge.getPermissionStates();
• adds a first-party LocalNetwork plugin exposing the standard
  checkPermissions()/requestPermissions() flow from JavaScript, with no
  app-side native code required.

Adds unit tests covering the API 37 boundary in PermissionHelper, the
Bridge permission state/validation behavior, and the LocalNetwork plugin
registration and pre-37 granted flow.

Closes #8613