Remove the "non-selected" path icon from the API Explorer view

[maisarissi]

Challenge

The current VS Code extension UI is too much polluted making harder for users to really find what they are looking for.

Proposal

Remove the "non-selected" path icon from the API Explorer.

Non-selected paths shouldn't have any icons and selected paths should show the check ✅ icon

Acceptance Criteria

1. All non-selected paths shouldn't have any icon but a blank space for the future check icon needs to be kept.
2. The indentation should still follow the current experience, so we don't confuse users when the ✅ icon is added, making the tree view hard to follow.
3. When creating a new plugin/client or just exploring an API, the OpenAPI should be loaded in the API explorer with no selected path.
4. When regenerating an existing plugin/client, the API should be loaded based on the current include/exclude paths and the right icons.

[maisarissi]

duplicated of: #5219