Hide the search mode picker until there's a query

The chats/messages picker has nothing to switch between before a query is
entered, so it only shows once the user starts searching.

ElementX/Sources/Screens/SearchScreen/View/SearchScreen.swift

@@ -40,14 +40,17 @@ struct SearchScreen: View {
                 .padding(.horizontal, 16)
                 .padding(.vertical, 8)
             
-            Picker(L10n.actionSearch, selection: $context.searchMode) {
-                ForEach(SearchScreenMode.allCases) { mode in
-                    Text(mode.title).tag(mode)
+            // There's nothing to switch between until the user searches for something.
+            if context.viewState.isSearching {
+                Picker(L10n.actionSearch, selection: $context.searchMode) {
+                    ForEach(SearchScreenMode.allCases) { mode in
+                        Text(mode.title).tag(mode)
+                    }
                 }
+                .pickerStyle(.segmented)
+                .padding(.horizontal, 16)
+                .padding(.bottom, 8)
             }
-            .pickerStyle(.segmented)
-            .padding(.horizontal, 16)
-            .padding(.bottom, 8)
             
             switch context.viewState.bindings.searchMode {
             case .rooms:

PreviewTests/Sources/__Snapshots__/PreviewTests/searchScreen.Empty-iPad-en-GB.png

@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:7bfea050d80105ee2383b4c53466ca42f2a17bebad5d8211882292f75803a3e2
-size 93453
+oid sha256:99f93030951c29a907a1097916bb5a783211e6f6fed89b9d7bda87a35a0f024c
+size 86970

PreviewTests/Sources/__Snapshots__/PreviewTests/searchScreen.Empty-iPad-pseudo.png

@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:e40f5ec001e372489b4ae212080364b779caaeb80e5cea0fbc42b0626d57e2a1
-size 100371
+oid sha256:bee04cd0aec01b6559ad6e76f6be1809950ee62fde425880d4efd5d7bbfebb6b
+size 92348

PreviewTests/Sources/__Snapshots__/PreviewTests/searchScreen.Empty-iPhone-en-GB.png

@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:2ad035e3a8905a8c16aa69cb6f7a640b022454812fd808eec45649995d85a4aa
-size 49390
+oid sha256:9d7e618d79d4a0c0fd7b931880f87ee000f57f75d52b51e50fd421bbc3a0a478
+size 44012

PreviewTests/Sources/__Snapshots__/PreviewTests/searchScreen.Empty-iPhone-pseudo.png

@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:37a6276be4d882858a34511cbc743154c84630e080835980d3744b5d5f6cf080
-size 60230
+oid sha256:a446fa6595aa3199c60a97ee3d4df423fcc2e07a2726343c3c0d1c12678d997f
+size 53981