[clangd] Add missing readonly modifier for const generic parameters

[tom-anders]

Summary

Fixes https://github.com/clangd/clangd/issues/1222. As discussed there, we saw no reason to keep this check.

[tom-anders]

Thanks!

clang-tools-extra/clangd/SemanticHighlighting.cpp

if (isa<ObjCObjectPointerType>(TP))
     return HighlightingKind::Class;
   if (auto *TD = TP->getAsTagDecl())
     return kindForDecl(TD, Resolver);
   return llvm::None;
 }
 
 // Whether T is const in a loose sense - is a variable with this type readonly?
 bool isConst(QualType T) {
-  if (T.isNull() || T->isDependentType())
+  if (T.isNull())
     return false;
   T = T.getNonReferenceType();
   if (T.isConstQualified())
     return true;
   if (const auto *AT = T->getAsArrayTypeUnsafe())
     return isConst(AT->getElementType());
   if (isConst(T->getPointeeType()))
     return true;

clang-tools-extra/clangd/unittests/SemanticHighlightingTests.cpp

)cpp",
         }
       )cpp",
       // Predefined identifiers
       R"cpp(
         void $Function_decl[[Foo]]() {
             const char *$LocalVariable_decl_readonly[[s]] = $LocalVariable_readonly_static[[__func__]];
         }
       )cpp",
+      // Issue 1022: readonly modifier for generic parameter
+      R"cpp(
+        template <typename $TemplateParameter_decl[[T]]>
+        auto $Function_decl[[foo]](const $TemplateParameter[[T]] $Parameter_decl_readonly[[template_type]], 
+                                   const $TemplateParameter[[auto]] $Parameter_decl_readonly[[auto_type]], 
+                                   const int $Parameter_decl_readonly[[explicit_type]]) {
+            return $Parameter_readonly[[template_type]] 
+                 + $Parameter_readonly[[auto_type]] 
+                 + $Parameter_readonly[[explicit_type]];
+        }
+      )cpp",
       // Explicit template specialization
       R"cpp(
         struct $Class_decl[[Base]]{};
         template <typename $TemplateParameter_decl[[T]]>
         struct $Class_decl[[S]] : public $Class[[Base]] {};
         template <> 
         struct $Class_decl[[S]]<void> : public $Class[[Base]] {};