fix(core): prevent removeListener from removing wrong listener

[maniktyagi04]

Description

Fixes #8269

When removeListener is called with a listener that doesn't exist, indexOf returns -1, and splice(-1, 1) removes the last element in the array. This PR adds a check to only splice if the listener is found.

Changes

• Added index validation in removeListener method
• Added test case to verify the fix

Testing

• ✅ All existing tests pass (51 tests in core)
• ✅ New test case verifies that removing a non-existent listener doesn't affect other listeners

Impact

• Type: Bug fix
• Breaking: No
• Platforms: Web (affects WebPlugin implementations)

Before

// Removing a non-existent listener would remove the last listener
await plugin.addListener('test', listener1);
await plugin.addListener('test', listener2);
await removeListener('test', listener3); // listener2 gets removed ❌

After

// Removing a non-existent listener does nothing
await plugin.addListener('test', listener1);
await plugin.addListener('test', listener2);
await removeListener('test', listener3); // No change ✅