depend upon and invoke upstream nushell code directly (not via spawning new nu processes)

[jokeyrhyme]

• we should explore this first, as it might not be worth the trade-offs
• how significant is the performance benefit?
• how frequently would upstream code break backwards compatibility (i.e. what is the ongoing burden)

[jokeyrhyme]

mentioned here: nushell/vscode-nushell-lang#117 (comment)

[jokeyrhyme]

From Discord: https://discord.com/channels/601130461678272522/1066353495638278194/1161785815710576700

we'd like to have nuls built into nushell. i'm guessing that probably means a nu-language-server crate in our main repo. we'd like to integrate more fully with nushell so that the language server doesn't have to shell out at all. it just accesses the functions that the --ide flags call. then we see it being run as nu --lsp. the key here is that people don't have to have any separate installs. if they have nushell, they have the language server. we're making this up as we go so who knows how that could change in the future.