debugger: Relax implementation of validate_config to not run validation (#31785)

When we moved to schema-based debug configs, we've added validate_config
- a trait method
that is supposed to both validate the configuration and determine
whether it is a launch configuration
or an attach configuration.

The validation bit is a bit problematic though - we received reports on
Discords about
scenarios not starting up properly; it turned out that Javascript's
implementation was overly strict.
Thus, I got rid of any code that tries to validate the config - let's
let the debug adapter itself
decide whether it can digest the configuration or not. validate_config
is now left unimplemented for most
DebugAdapter implementations (except for PHP), because all adapters use
`request`: 'launch'/'attach' for that.
Let's leave the trait method in place though, as nothing guarantees this
to be true for all adapters.

cc @Anthony-Eid

Release Notes:

- debugger: Improved error messages when the debug scenario is not
valid.
- debugger: Fixed cases where valid configs were rejected.

crates/debugger_ui/src/tests/new_session_modal.rs

@@ -322,7 +322,7 @@ async fn test_dap_adapter_config_conversion_and_validation(cx: &mut TestAppConte
         );
 
         let request_type = adapter
-            .validate_config(&debug_scenario.config)
+            .request_kind(&debug_scenario.config)
             .unwrap_or_else(|_| {
                 panic!(
                     "Adapter {} should validate the config successfully",