nvim: Add mason env utility function

Should return the mason environment for lsp servers to be able to set it
in the 'core/languages.lua' list.

However, currently it is initialized too early (I think), before
mason.nvim, and thus never gets the initialized env var.

nvim/.config/nvim/lua/core/languages.lua

@@ -1,8 +1,8 @@
 -- A list of all languages for which I have support for any of:
--- an LSP
--- Treesitter
--- linting
--- formatting
+-- an LSP (lsp)
+-- Treesitter (ts)
+-- linting (lint)
+-- formatting (format)
 --
 -- with their respective names used by lspconfig, nvim-treesitter, nvim-lint and conform.
 --
@@ -12,6 +12,16 @@ if vim.fn.executable("nufmt") == 1 then
 	nushell.format = { nu = { "nufmt" } }
 end
 
+-- FIXME: This does not work for populating LSP config,
+-- never gets set MASON env var. Executing too early?
+local function mason_dir()
+	local dir = vim.fn.getenv("MASON")
+	if dir ~= vim.NIL then
+		return dir
+	end
+	return vim.fn.getenv("HOME") .. "/.local/share/nvim/mason"
+end
+
 local languages = {
 	arduino = { lsp = { arduino_language_server = {} }, ts = { "arduino" } },
 	awk = { ts = { "awk" }, format = { awk = { "gawk" } } },