video_core/ast: Replace std::string with a constexpr std::string_view

Same behavior, but without the need to heap allocate

src/video_core/shader/ast.cpp

@@ -350,11 +350,9 @@ private:
     std::string tabs_memo{};
     u32 memo_scope{};
 
-    static std::string tabs;
+    static constexpr std::string_view tabs{"                                    "};
 };
 
-std::string ASTPrinter::tabs = "                                    ";
-
 std::string ASTManager::Print() {
     ASTPrinter printer{};
     printer.Visit(main_node);