fix(health): misleading warnings re filetypes registered w/ vim.filetype.add() #38867
Problem:
`:checkhealth vim.lsp` validates configured filetypes against
`getcompletion('', 'filetype')`. This only reflects runtime support
files.
This causes false warnings in `:checkhealth vim.lsp` for configured
filetypes that are known to the Lua filetype registry, including
values added with `vim.filetype.add()` and built-in registry-only
filetypes.
Solution:
Build the healthcheck's known-filetype set from both
`getcompletion('', 'filetype')` and `vim.filetype.inspect()`.
(cherry picked from commit 20a3254ad4)
Co-authored-by: Barrett Ruth <62671086+barrettruth@users.noreply.github.com>
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