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/session/running.rs

@@ -812,7 +812,7 @@ impl RunningState {
             let request_type = dap_registry
                 .adapter(&adapter)
                 .ok_or_else(|| anyhow!("{}: is not a valid adapter name", &adapter))
-                .and_then(|adapter| adapter.validate_config(&config));
+                .and_then(|adapter| adapter.request_kind(&config));
 
             let config_is_valid = request_type.is_ok();
 
@@ -954,7 +954,10 @@ impl RunningState {
                 config = scenario.config;
                 Self::substitute_variables_in_config(&mut config, &task_context);
             } else {
-                anyhow::bail!("No request or build provided");
+                let Err(e) = request_type else {
+                    unreachable!();
+                };
+                anyhow::bail!("Zed cannot determine how to run this debug scenario. `build` field was not provided and Debug Adapter won't accept provided configuration because: {e}");
             };
 
             Ok(DebugTaskDefinition {