Add Mojo support

[yosefahab]

Is your feature request related to a problem? Please describe.

Mojo configuration has been added as a locally installed server in 2804, and hence can be configured using lspconfig as:

lspconfig["mojo"].setup({
	cmd = { 'mojo-lsp-server' },
	root_dir = util.find_git_ancestor,
	single_file_support = true,
	capabilities = capabilities,
	on_attach = function(client, bufnr)
		on_attach(client, bufnr)
		vim.keymap.set("n", "<leader>fmt",
			function() vim.cmd("noa silent !mojo format --quiet " .. vim.fn.expand("%:p")) end) -- manually format document
	end,
	filetypes = { "mojo", "*.🔥" },
})

mason-lspconfig complains that the server name is not valid: [mason-lspconfig.nvim] Server "mojo" is not a valid entry in ensure_installed. Make sure to only provide lspconfig server names..

Describe the solution you'd like

Add a mapping for "mojo" to "mojo-lsp-server".

Describe potential alternatives you've considered

Current workaround is configuring mojo from lspconfig, directly bypassing mason-lspconfig as described above.

Additional context

No response