Implement fold.at.else code folding property

[magicdmer]

如下代码，希望 #if到#else是一个代码折叠，然后#else到#endif是一个代码折叠，和vscode一样

#if 0
    printf("test1");
#else
    printf("test2");
#endif

[zufuliu]

The "fold.at.else" code folding property is not implemented (some were removed in 56083e026034ec8f7107552ac76dca88fc5da6aa).