I made a package to show call hierarchy and type hierarchy

[condy0919]

This package is primarily intended as a replacement for lsp-treemacs, which is quite heavyweight and relies on many external components. In contrast, lsp-hierarchy has only one external dependency—lsp-mode—while all other dependencies are built-in Emacs features. I would like to merge it into lsp-mode as a lightweight alternative to lsp-treemacs-type-hierarchy and lsp-treemacs-call-hierarchy.

[jcs090218]

I like the idea of having a lightweight alternative to lsp-treemacs, so I have no problem merging this to core.