Align accessibility IDs with elementX android (#567)

* Rename onboarding and login user/pass accessibility ids.

* Refactor remaining server change accessibility IDs

* Avoid accessibilityIdentifier spreading to all decorations on the textBox.

Required because otherwise there are multiple items tagged with the accessibilityId
which means we can't click on "the" item.

* Move all accessibility identifiers to `AccessibilityIdentifiers.swft`
- use same naming convention on all of them
- remove the unused ones
- fix build errors in integration tests and invalid identifiers (still broken until autodiscovery lands on rosa)

---------

Co-authored-by: Stefan Ceriu <stefanc@matrix.org>

ElementX/Sources/Screens/OnboardingScreen/View/OnboardingScreen.swift

@@ -47,7 +47,7 @@ struct OnboardingScreen: View {
                             // Add a hidden page at the start of the carousel duplicating the content of the last page
                             OnboardingPageView(content: context.viewState.content[pageCount - 1])
                                 .frame(width: geometry.size.width)
-                                .accessibilityIdentifier("hiddenPage")
+                                .accessibilityIdentifier(A11yIdentifiers.onboardingScreen.hidden)
                             
                             ForEach(0..<pageCount, id: \.self) { index in
                                 OnboardingPageView(content: context.viewState.content[index])
@@ -93,7 +93,7 @@ struct OnboardingScreen: View {
                 Text(ElementL10n.loginContinue)
             }
             .buttonStyle(.elementAction(.xLarge))
-            .accessibilityIdentifier("getStartedButton")
+            .accessibilityIdentifier(A11yIdentifiers.onboardingScreen.signIn)
         }
         .padding(.horizontal, verticalSizeClass == .compact ? 128 : 24)
         .readableFrame()