- [x] I have searched the [issues](https://github.com/apache/dubbo/issues) of this repository and believe that this is not a duplicate.
- [x] I have checked the [FAQ](https://github.com/apache/dubbo/blob/master/FAQ.md) of this repository and believe that this is not a duplicate.

### Environment

* Dubbo version: master
* Operating System version: windows
* Java version: 1.8

In ExtensionLoader, EXTENSION INSTANCES is a ConcurrentHashMap with a default size, and the extension class provided in Dubbo has exceeded 16. 
Start the program, it will expand at least twice. I think it is more appropriate to add an initial size of 64 here. 
Other places where ConcurrentHashMap is used should also pay attention to a suitable initial size
}
    public static void destroyAll() {
        EXTENSION_INSTANCES.forEach((_type, instance) -> {
            if (instance instanceof Lifecycle) {
                Lifecycle lifecycle = (Lifecycle) instance;
                try {
                    lifecycle.destroy();
                } catch (Exception e) {
                    logger.error("Error destroying extension " + lifecycle, e);
                }
            }
        });
    }
    private static ClassLoader findClassLoader() {
        return ClassUtils.getClassLoader(ExtensionLoader.class);
    }
    public String getExtensionName(T extensionInstance) {
        return getExtensionName(extensionInstance.getClass());
    }
    public String getExtensionName(Class<?> extensionClass) {
        getExtensionClasses();
        return cachedNames.get(extensionClass);
    }
    /**
     * This is equivalent to {@code getActivateExtension(url, key, null)}
     *
     * @param url url
     * @param key url parameter key which used to get extension point names
     * @return extension list which are activated.
     * @see #getActivateExtension(org.apache.dubbo.common.URL, String, String)