[libc++] Refactor how we do amortized growth

[philnik777]

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git-clang-format --diff origin/main HEAD --extensions  -- libcxx/include/string --diff_from_common_commit

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diff --git a/libcxx/include/string b/libcxx/include/string
index e4020b46e..bc334257a 100644
--- a/libcxx/include/string
+++ b/libcxx/include/string
@@ -2299,7 +2299,7 @@ private:
       return std::max(__required_size, 2 * __current_cap);
     }();
 
-    __long __buffer = __allocate_long_buffer(__alloc_, __new_cap);
+    __long __buffer  = __allocate_long_buffer(__alloc_, __new_cap);
     __buffer.__size_ = __required_size;
     return __buffer;
   }