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)

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

UITests/Sources/UserSessionScreenTests.swift

@@ -26,7 +26,7 @@ class UserSessionScreenTests: XCTestCase {
 
         app.assertScreenshot(.userSessionScreen, step: 1)
         
-        app.buttons["roomName:\(roomName)"].tap()
+        app.buttons[A11yIdentifiers.homeScreen.roomName(roomName)].tap()
         
         XCTAssert(app.staticTexts[roomName].waitForExistence(timeout: 5.0))