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/dap_adapters/src/gdb.rs

@@ -178,7 +178,7 @@ impl DebugAdapter for GdbDebugAdapter {
         let gdb_path = user_setting_path.unwrap_or(gdb_path?);
 
         let request_args = StartDebuggingRequestArguments {
-            request: self.validate_config(&config.config)?,
+            request: self.request_kind(&config.config)?,
             configuration: config.config.clone(),
         };