nvim feature tracking v0.8+

[jdhao]

1. splitkeep option
   neovim/neovim@5acf52e

2. new option linematch added for diffopt
   neovim/neovim@04fbb1d
   Use it like this set diffopt+=linematch:60, doc here.

3. float win title
   Float wins now can show title and customize its position, highlight as well since neovim/neovim@1af4bd0.

4. Create intermediate directory when writing file
   neovim/neovim@d337814
   When write a file, you can use :write ++p foo/bar/baz/test.txt, the intermediate directory will be created. The writefile() function now also accept p as flag.

5. cscope support removed feat(cscope)!: remove neovim/neovim#20545.
   cscope is like a pre-history code intelligence engine for writing c code, before the advent of LSP.

6. highlight code in help doc via treesitter
   neovim/neovim@0b05bd8

7. semantic token support in LSP
   LSP: semantic tokens support neovim/neovim#21100

[max397574]

added suffix option to diagnostics virtual text and float neovim/neovim#21130 and neovim/neovim#21140

news.txt with info about many changes https://github.com/neovim/neovim/blob/master/runtime/doc/news.txt

added function to show treesitter abstract syntax tree neovim/neovim#21322

[jdhao]

inspect highlight group under cursor (including ext mark): neovim/neovim@ef91146