Indicate boolean value for configured experimental features on startup (#74691)
When printing the configured experimental features of the Next.js config, we are currently not discriminating `true` from `false` values. This is especially confusing when disabling an experimental feature that is enabled by default. In this case it appears in the output as if the feature was enabled.
By using `✓` and `⨯` for boolean feature flags (and `·` for others), users can now clearly see whether a configured feature is enabled or disabled.
**Before:**
<img width="377" alt="before" src="https://github.com/user-attachments/assets/9cb75c1a-910d-48d2-ba1e-048213523e5f" />
**After:**
<img width="377" alt="after" src="https://github.com/user-attachments/assets/9975366d-b8fd-48ef-83e3-44fbad633f48" />