[android_intent] Make action optional, as Intents can also resolve with just the component name

[ened]

Description

Android Intents can also be constructed with just the component name like so:

final Intent intent = new Intent();
intent.setComponent(componentName);
context.startActivity(intent);

Effectively, if the developer knows the target component, it can be called directly.

Related Issues

Preparation work for flutter/flutter#51942, which adds a "canResolve" method.

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Breaking Change

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[matthew-carroll]

Would you mind adding e2e tests that launch relevant Intent configurations to ensure that the platform side of the plugin operates correctly, too?

[ened]

@matthew-carroll there are no e2e tests per se as they would launch another Android App potentially. There is a rather large unit test for the MethodHandler implementation that uses Robolectric to verify. I added an additional case in there for the "no-action, but component name" use case.