[clangd][c++20] Add concept semantic highlighting test case

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

)cpp",
       struct $Class_def[[F]] {
         void $Method_def[[foo]]() {};
       };
       $Concept[[Fooable]] $Class_deduced[[auto]] $Variable_def[[f]] = $Class[[F]]();
 
       void $Function_def[[Bar]]($Concept[[Fooable]] $TemplateParameter[[auto]] $Parameter_def[[x]]) {}
 
       template$Bracket[[<]]$Concept[[Fooable]] auto $TemplateParameter_def_readonly[[x]]$Bracket[[>]] void $Function_def[[Boo]]() {}
+      bool $Variable_def[[b]] = $Concept[[Fooable]]$Bracket[[<]]int$Bracket[[>]];
     )cpp",
       // Dependent template name
       R"cpp(
       template $Bracket[[<]]template $Bracket[[<]]typename$Bracket[[>]] class$Bracket[[>]] struct $Class_def[[A]] {};
       template $Bracket[[<]]typename $TemplateParameter_def[[T]]$Bracket[[>]]
       using $Typedef_decl[[W]] = $Class[[A]]$Bracket[[<]]
         $TemplateParameter[[T]]::template $Class_dependentName[[Waldo]]
       $Bracket[[>]];
)cpp",
       R"cpp(
         class $Class_def_abstract[[Base]] { virtual void $Method_decl_abstract_virtual[[m]]() = 0; };
         class $Class_def[[override]] : public $Class_abstract[[Base]] { void $Method_decl_virtual[[m]]() $Modifier[[override]]; };
         class $Class_def[[final]] : public $Class[[override]] { void $Method_decl_virtual[[m]]() $Modifier[[override]] $Modifier[[final]]; };
       )cpp",
       // Issue 1222: readonly modifier for generic parameter
       R"cpp(
         template $Bracket[[<]]typename $TemplateParameter_def[[T]]$Bracket[[>]]
-        auto $Function_def[[foo]](const $TemplateParameter[[T]] $Parameter_def_readonly[[template_type]], 
-                                  const $TemplateParameter[[auto]] $Parameter_def_readonly[[auto_type]], 
+        auto $Function_def[[foo]](const $TemplateParameter[[T]] $Parameter_def_readonly[[template_type]],
+                                  const $TemplateParameter[[auto]] $Parameter_def_readonly[[auto_type]],
                                   const int $Parameter_def_readonly[[explicit_type]]) {
-            return $Parameter_readonly[[template_type]] 
+            return $Parameter_readonly[[template_type]]
                  $Operator_userDefined[[+]] $Parameter_readonly[[auto_type]]
                  $Operator_userDefined[[+]] $Parameter_readonly[[explicit_type]];
         }
       )cpp",
       // Explicit template specialization
       R"cpp(
         struct $Class_def[[Base]]{};
         template $Bracket[[<]]typename $TemplateParameter_def[[T]]$Bracket[[>]]
$Bracket[[>]] $LocalVariable_def[[s7]];
         class $Class_def[[A]] {
           enum class $Enum_decl[[E]];
         };
         template $Bracket[[<]]typename $TemplateParameter_def[[T]]$Bracket[[>]]
         enum class $Class[[A]]$Bracket[[<]]$TemplateParameter[[T]]$Bracket[[>]]::$Enum_decl[[E]] {$EnumConstant_decl_readonly[[X]], $EnumConstant_decl_readonly[[Y]], $EnumConstant_decl_readonly[[Z]]};
         template $Bracket[[<]]class $TemplateParameter_def[[T]]$Bracket[[>]]
         class $Class_def[[B]] {
           template $Bracket[[<]]class $TemplateParameter_def[[U]]$Bracket[[>]] void $Method_def[[foo]]($TemplateParameter[[U]]) { }
-          template$Bracket[[<]]$Bracket[[>]] void $Method_def[[foo]]$Bracket[[<]]int$Bracket[[>]](int) { } 
+          template$Bracket[[<]]$Bracket[[>]] void $Method_def[[foo]]$Bracket[[<]]int$Bracket[[>]](int) { }
           friend void $Function_decl[[foo]]$Bracket[[<]]$Bracket[[>]]($TemplateParameter[[T]]);
         };
       )cpp",
       // Brackets support: Function calls
       R"cpp(
         template $Bracket[[<]]typename$Bracket[[>]] void $Function_decl[[free]]();
         template $Bracket[[<]]typename $TemplateParameter_def[[T]]$Bracket[[>]]
           struct $Class_def[[A]] {