Fix duplicated type annotation suggestion

Before, there was more or less duplicated suggestions to add type hints.
Fix by clearing more generic suggestions when a more specific suggestion
is possible.

This fixes #93506 .

compiler/rustc_errors/src/diagnostic.rs

@@ -614,6 +614,14 @@ impl Diagnostic {
         self
     }
 
+    /// Clear any existing suggestions.
+    pub fn clear_suggestions(&mut self) -> &mut Self {
+        if let Ok(suggestions) = &mut self.suggestions {
+            suggestions.clear();
+        }
+        self
+    }
+
     /// Helper for pushing to `self.suggestions`, if available (not disable).
     fn push_suggestion(&mut self, suggestion: CodeSuggestion) {
         if let Ok(suggestions) = &mut self.suggestions {

compiler/rustc_errors/src/diagnostic_builder.rs

@@ -461,6 +461,7 @@ impl<'a, G: EmissionGuarantee> DiagnosticBuilder<'a, G> {
     forward!(pub fn set_is_lint(&mut self,) -> &mut Self);
 
     forward!(pub fn disable_suggestions(&mut self,) -> &mut Self);
+    forward!(pub fn clear_suggestions(&mut self,) -> &mut Self);
 
     forward!(pub fn multipart_suggestion(
         &mut self,

compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs

@@ -2074,6 +2074,9 @@ impl<'a, 'tcx> InferCtxtPrivExt<'a, 'tcx> for InferCtxt<'a, 'tcx> {
                         //    |
                         //    = note: cannot satisfy `_: Tt`
 
+                        // Clear any more general suggestions in favor of our specific one
+                        err.clear_suggestions();
+
                         err.span_suggestion_verbose(
                             span.shrink_to_hi(),
                             &format!(