Establish baseline webdriver conformance results (#35024)

https://github.com/web-platform-tests/wpt/pull/50041 allows us to start
running the webdriver conformance tests in Servo, which will make it
easier for us to track regressions/improvements in our webdriver server
implementation.

---
- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [x] These changes are part of #15274
- [x] There are tests for these changes

---------

Signed-off-by: Josh Matthews <josh@joshmatthews.net>

components/webdriver_server/capabilities.rs

@@ -4,7 +4,7 @@
 
 use serde_json::{Map, Value};
 use webdriver::capabilities::{BrowserCapabilities, Capabilities};
-use webdriver::error::{WebDriverError, WebDriverResult};
+use webdriver::error::{ErrorStatus, WebDriverError, WebDriverResult};
 
 pub struct ServoCapabilities {
     pub browser_name: String,
@@ -79,42 +79,42 @@ impl BrowserCapabilities for ServoCapabilities {
         &mut self,
         _: &serde_json::Map<std::string::String, Value>,
     ) -> Result<bool, WebDriverError> {
-        todo!()
+        Err(WebDriverError::new(ErrorStatus::UnsupportedOperation, ""))
     }
 
     fn webauthn_virtual_authenticators(
         &mut self,
         _: &serde_json::Map<std::string::String, Value>,
     ) -> Result<bool, WebDriverError> {
-        todo!()
+        Err(WebDriverError::new(ErrorStatus::UnsupportedOperation, ""))
     }
 
     fn webauthn_extension_uvm(
         &mut self,
         _: &serde_json::Map<std::string::String, Value>,
     ) -> Result<bool, WebDriverError> {
-        todo!()
+        Err(WebDriverError::new(ErrorStatus::UnsupportedOperation, ""))
     }
 
     fn webauthn_extension_prf(
         &mut self,
         _: &serde_json::Map<std::string::String, Value>,
     ) -> Result<bool, WebDriverError> {
-        todo!()
+        Err(WebDriverError::new(ErrorStatus::UnsupportedOperation, ""))
     }
 
     fn webauthn_extension_large_blob(
         &mut self,
         _: &serde_json::Map<std::string::String, Value>,
     ) -> Result<bool, WebDriverError> {
-        todo!()
+        Err(WebDriverError::new(ErrorStatus::UnsupportedOperation, ""))
     }
 
     fn webauthn_extension_cred_blob(
         &mut self,
         _: &serde_json::Map<std::string::String, Value>,
     ) -> Result<bool, WebDriverError> {
-        todo!()
+        Err(WebDriverError::new(ErrorStatus::UnsupportedOperation, ""))
     }
 }