fix(TokenSelector): Duplicate plain token entries

- filter out plain tokens from the adaptor's if already present in the
output model
- add a corresponding regression test

Fixes #15412

storybook/pages/TokenSelectorPage.qml

@@ -46,6 +46,14 @@ SplitView {
             image: "https://etherscan.io/token/images/horizonstate2_28.png"
             communityId: ""
         }
+        // DAI should be filtered out
+        ListElement {
+            key: "DAI"
+            name: "Dai Stablecoin"
+            symbol: "DAI"
+            image: ""
+            communityId: ""
+        }
     }
 
     QtObject {

storybook/qmlTests/tests/tst_TokenSelectorViewAdaptor.qml

@@ -22,6 +22,14 @@ Item {
             image: "https://cryptologos.cc/logos/aave-aave-logo.png"
             communityId: ""
         }
+        // DAI should be filtered out
+        ListElement {
+            key: "DAI"
+            name: "Dai Stablecoin"
+            symbol: "DAI"
+            image: ""
+            communityId: ""
+        }
     }
 
     QtObject {
@@ -133,5 +141,16 @@ Item {
             // should have ~45.90 balance
             fuzzyCompare(delegate.currencyBalance, 45.90, 0.01)
         }
+
+        function test_duplicatePlainTokens() {
+            verify(!!controlUnderTest)
+
+            controlUnderTest.showAllTokens = true
+            const searchText = "DAI"
+            controlUnderTest.searchString = searchText
+
+            // search yields 1 result
+            tryCompare(controlUnderTest.outputAssetsModel, "count", 1)
+        }
     }
 }

ui/app/AppLayouts/Wallet/adaptors/TokenSelectorViewAdaptor.qml

@@ -106,6 +106,21 @@ QObject {
                 roleName: "communityId"
                 value: ""
                 enabled: !root.showCommunityAssets
+            },
+            // duplicate tokens filter
+            FastExpressionFilter {
+                function hasDuplicateKey(tokensKey) {
+                    return ModelUtils.indexOf(assetsObjectProxyModel, "tokensKey", tokensKey) > -1
+                }
+
+                expression: {
+                    if (model.which_model === "plain_tokens_model") {
+                        return !hasDuplicateKey(model.tokensKey)
+                    }
+                    return true
+                }
+                expectedRoles: ["which_model", "tokensKey"]
+                enabled: root.showAllTokens
             }
         ]