5687: Fix document symbols order r=matklad a=magurotuna
Resolves#5655
And adds tests for `handle_document_symbol`, both with `hierarchical_symbols` enabled and with it disabled.
Previously document symbols were displayed in reverse order in sublime text with its LSP plugin, but this patch fixes it like this:

Co-authored-by: Yusuke Tanaka <yusuktan@maguro.dev>