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/php.rs

@@ -94,7 +94,7 @@ impl PhpDebugAdapter {
             envs: HashMap::default(),
             request_args: StartDebuggingRequestArguments {
                 configuration: task_definition.config.clone(),
-                request: <Self as DebugAdapter>::validate_config(self, &task_definition.config)?,
+                request: <Self as DebugAdapter>::request_kind(self, &task_definition.config)?,
             },
         })
     }
@@ -282,10 +282,7 @@ impl DebugAdapter for PhpDebugAdapter {
         Some(SharedString::new_static("PHP").into())
     }
 
-    fn validate_config(
-        &self,
-        _: &serde_json::Value,
-    ) -> Result<StartDebuggingRequestArgumentsRequest> {
+    fn request_kind(&self, _: &serde_json::Value) -> Result<StartDebuggingRequestArgumentsRequest> {
         Ok(StartDebuggingRequestArgumentsRequest::Launch)
     }