Refactor plugin: Prefer code action

`isPreferred` can influence the client side order of code actions. The
idea is that an unused import is likely to be removed and less likely
the warning will be disabled. Therefore actions to remove a single or
all redundant imports should be preferred, so that the client can
prioritize them higher.

Followup of
<haskell#3018>

plugins/hls-refactor-plugin/src/Development/IDE/Plugin/CodeAction.hs

@@ -389,7 +389,7 @@ suggestHideShadow ps fileContents mTcM mHar Diagnostic {_message, _range}
   | otherwise = []
   where
     L _ HsModule {hsmodImports} = astA ps
- 
+
     suggests identifier modName s
       | Just tcM <- mTcM,
         Just har <- mHar,
@@ -458,6 +458,12 @@ suggestRemoveRedundantImport ParsedModule{pm_parsed_source = L _  HsModule{hsmod
         = [("Remove import", [TextEdit (extendToWholeLineIfPossible contents _range) ""])]
     | otherwise = []
 
+
+-- Note [Removing imports is preferred]
+-- It's good to prefer the remove imports code action because an unused import
+-- is likely to be removed and less likely the warning will be disabled.
+-- Therefore actions to remove a single or all redundant imports should be
+-- preferred, so that the client can prioritize them higher.
 caRemoveRedundantImports :: Maybe ParsedModule -> Maybe T.Text -> [Diagnostic] -> [Diagnostic] -> Uri -> [Command |? CodeAction]
 caRemoveRedundantImports m contents digs ctxDigs uri
   | Just pm <- m,
@@ -481,7 +487,8 @@ caRemoveRedundantImports m contents digs ctxDigs uri
         _diagnostics = Nothing
         _documentChanges = Nothing
         _edit = Just WorkspaceEdit{..}
-        _isPreferred = Nothing
+        -- See Note [Removing imports is preferred]
+        _isPreferred = Just True
         _command = Nothing
         _disabled = Nothing
         _xdata = Nothing
@@ -520,7 +527,8 @@ caRemoveInvalidExports m contents digs ctxDigs uri
         _documentChanges = Nothing
         _edit = Just WorkspaceEdit{..}
         _command = Nothing
-        _isPreferred = Nothing
+        -- See Note [Removing imports is preferred]
+        _isPreferred = Just True
         _disabled = Nothing
         _xdata = Nothing
         _changeAnnotations = Nothing
@@ -534,7 +542,8 @@ caRemoveInvalidExports m contents digs ctxDigs uri
         _documentChanges = Nothing
         _edit = Just WorkspaceEdit{..}
         _command = Nothing
-        _isPreferred = Nothing
+        -- See Note [Removing imports is preferred]
+        _isPreferred = Just True
         _disabled = Nothing
         _xdata = Nothing
         _changeAnnotations = Nothing