fix(fold): don't include whitespace end regions

Some languages that are difficult to parse via Treesitter may
incorrectly include whitespace lines at the end of regions. This can
makes the calculated folds sub-optimal.

To recitfy, use a custom directive (trim), to calculate the range with
the trailing whitespace lines removed. Note this only works if the
region end column is 0.

Also added folds for Make.

lua/nvim-treesitter/query_predicates.lua

@@ -153,3 +153,36 @@ query.add_directive("exclude_children!", function(match, _pattern, _bufnr, pred,
   end
   metadata.content = ranges
 end)
+
+-- Trim blank lines from end of the region
+-- Arguments are the captures to trim.
+query.add_directive("trim!", function(match, _, bufnr, pred, metadata)
+  for _, id in ipairs { select(2, unpack(pred)) } do
+    local node = match[id]
+    local start_row, start_col, end_row, end_col = node:range()
+
+    -- Don't trim if region ends in middle of a line
+    if end_col ~= 0 then
+      return
+    end
+
+    while true do
+      -- As we only care when end_col == 0, always inspect one line above end_row.
+      local end_line = vim.api.nvim_buf_get_lines(bufnr, end_row - 1, end_row, true)[1]
+
+      if end_line ~= "" then
+        break
+      end
+
+      end_row = end_row - 1
+    end
+
+    -- If this produces an invalid range, we just skip it.
+    if start_row < end_row or (start_row == end_row and start_col <= end_col) then
+      if not metadata[id] then
+        metadata[id] = {}
+      end
+      metadata[id].range = { start_row, start_col, end_row, end_col }
+    end
+  end
+end)