AK: Avoid a copy in StringBuilder's default constructor

Author: https://github.com/LucasChollet
Commit: b844f3219e
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/5098
Reviewed-by: https://github.com/gmta ✅

AK/StringBuilder.cpp

@@ -41,8 +41,9 @@ ErrorOr<StringBuilder> StringBuilder::create(size_t initial_capacity)
 }
 
 StringBuilder::StringBuilder()
-    : StringBuilder(inline_capacity)
 {
+    static_assert(inline_capacity > STRING_BASE_PREFIX_SIZE);
+    m_buffer.resize(STRING_BASE_PREFIX_SIZE);
 }
 
 StringBuilder::StringBuilder(size_t initial_capacity)