Encrypt the page data contents. Page type can't be FIL_PAGE_ENCRYPTED, FIL_PAGE_COMPRESSED_AND_ENCRYPTED,FIL_PAGE_ENCRYPTED_RTREE.是加密页面数据内容。 页面类型不能
Shouldn't encrypte an already encrypted page. 不应该加密已经加密的页面。
This is data size which need to encrypt 这是需要加密的数据大小
Only encrypt the data + trailer, leave the header alone 只加密数据+预告片，单独留下标题
Copy remain bytes and page tailer. 复制保留字节和页面预告片。
Encrypt the remain bytes. 加密剩余的字节。
Copy the header as is. 按原样复制标题。
Add encryption control information. Required for decrypting. 添加加密控制信息。 解密需要。
If the page is compressed, we don't need to save theoriginal type, since it is done in compression already. 如果页面被压缩，我们不需要保存原始类型，因为它已经在压缩中完成了。
If the page is R-tree page, we need to save original type. 如果页面是R-tree页面，我们需要保存原始类型。、