[Feature] Detecting if DBC path is valid

**Is your feature request related to a problem? Please describe.**
Currently user can put any path in DBC textbox and WDE will silently fail if the path do not contain valid DBC.

**Describe the solution you'd like**
Before saving, it should try to detect if path contains valid dbc. Checking for required files (without looking into the content) is enough.

Start at the DBC textbox and the save flow to find where the path is accepted. Identify the required files that define a valid DBC path, then verify that invalid paths are rejected before saving while valid paths continue successfully.

Written by the indexing model from the issue text.