Added custom error message when trying to assign constraint type to generic type parameter (#30394)

* Added custom error message when trying to assign constraint type to generic type parameter

Fixes #29049.

This also adds the new message in chained error messages. `typeParameterDiamond4.errors.txt` shows it appearing twice in the "diamond" scenario. I can't tell if this severely increased amount of nested messages is good or bad...?

* Updated diagnostic message per suggestion

* Align formatting with local custom

src/compiler/checker.ts

@@ -12328,6 +12328,15 @@ namespace ts {
             function reportRelationError(message: DiagnosticMessage | undefined, source: Type, target: Type) {
                 const [sourceType, targetType] = getTypeNamesForErrorDisplay(source, target);
 
+                if (target.flags & TypeFlags.TypeParameter && target.immediateBaseConstraint !== undefined && isTypeAssignableTo(source, target.immediateBaseConstraint)) {
+                    reportError(
+                        Diagnostics._0_is_assignable_to_the_constraint_of_type_1_but_1_could_be_instantiated_with_a_different_subtype_of_constraint_2,
+                        sourceType,
+                        targetType,
+                        typeToString(target.immediateBaseConstraint),
+                    );
+                }
+
                 if (!message) {
                     if (relation === comparableRelation) {
                         message = Diagnostics.Type_0_is_not_comparable_to_type_1;

src/compiler/diagnosticMessages.json

@@ -3096,6 +3096,10 @@
         "category": "Error",
         "code": 5074
     },
+    "'{0}' is assignable to the constraint of type '{1}', but '{1}' could be instantiated with a different subtype of constraint '{2}'.": {
+        "category": "Error",
+        "code": 5075
+    },
 
     "Generates a sourcemap for each corresponding '.d.ts' file.": {
         "category": "Message",