[Verify Session] Add missing 'start verification' screen. (#241)

* Add missing 'start verification' screen. 
* Fix retries sometimes not working because of `SessionVerificationController.setDelegate`.
* Make the negative button invisible when not needed.

libraries/matrix/impl/src/main/kotlin/io/element/android/libraries/matrix/impl/verification/RustSessionVerificationService.kt

@@ -38,6 +38,7 @@ class RustSessionVerificationService @Inject constructor() : SessionVerification
             _isReady.value = value != null
             // If status was 'Unknown', move it to either 'Verified' or 'NotVerified'
             if (value != null) {
+                value.setDelegate(this)
                 updateVerificationStatus(value.isVerified())
             }
         }
@@ -52,7 +53,6 @@ class RustSessionVerificationService @Inject constructor() : SessionVerification
     override val sessionVerifiedStatus: StateFlow<SessionVerifiedStatus> = _sessionVerifiedStatus.asStateFlow()
 
     override fun requestVerification() = tryOrFail {
-        verificationController?.setDelegate(this)
         verificationController?.requestVerification()
     }
 
@@ -63,7 +63,6 @@ class RustSessionVerificationService @Inject constructor() : SessionVerification
     override fun declineVerification() = tryOrFail { verificationController?.declineVerification() }
 
     override fun startVerification() = tryOrFail {
-        verificationController?.setDelegate(this)
         verificationController?.startSasVerification()
     }
 

libraries/ui-strings/src/main/res/values/strings_eax.xml

@@ -47,6 +47,7 @@
 
     <string name="verification_positive_button_initial">I am ready</string>
     <string name="verification_positive_button_canceled">Retry verification</string>
+    <string name="verification_positive_button_ready">Start</string>
     <string name="verification_positive_button_verifying_start">They match</string>
     <string name="verification_positive_button_verifying_ongoing">Waiting to match</string>