modules/lsp/servers: move to dedicated file/dir

Move the code related to the `lsp.servers` option into a dedicated module,
cleaning up `modules/lsp/default.nix`.

modules/lsp/servers/global-server.nix

@@ -0,0 +1,49 @@
+{ lib, ... }:
+let
+  inherit (lib) types;
+in
+{
+  options = {
+    enable = lib.mkOption {
+      type = types.bool;
+      description = "Whether to enable global defaults shared by all servers.";
+      default = true;
+      example = false;
+    };
+
+    name = lib.mkOption {
+      type = types.str;
+      description = ''
+        The name to use for global defaults shared by all servers.
+
+        Supplied to functions like `vim.lsp.config()`.
+
+        Will always be `"*"`.
+      '';
+      readOnly = true;
+    };
+
+    settings = lib.mkOption {
+      type = with types; attrsOf anything;
+      description = ''
+        Default configuration shared by all servers.
+
+        Will be merged by neovim using the behaviour of [`vim.tbl_deep_extend()`](https://neovim.io/doc/user/lua.html#vim.tbl_deep_extend()).
+      '';
+      default = { };
+      example = {
+        root_markers = [ ".git" ];
+        capabilities.textDocument.semanticTokens = {
+          multilineTokenSupport = true;
+        };
+      };
+    };
+  };
+
+  imports = [
+    ./server-renames.nix
+  ];
+
+  # Define the read-only `name` here, instead of via `default`, to avoid documenting it twice
+  config.name = "*";
+}