feat: Inject object count defaults into user table

This commit introduces a function to inject default properties for
certain object types into a user-provided table of such properties, just
in case the user did not provide them. This allows the user to only
override what they want for the object types they want to be counted.

lua/mkdnflow/foldtext.lua

@@ -224,8 +224,28 @@ local count_blocks = function(line_objs)
     return counts
 end
 
+-- Function to inject defaults for any object type for which the user didn't specify necessary
+-- information. Not using tbl_deep_extend here since we don't want to add object types that the user
+-- doesn't want, if they have specified their own count opts table.
+local inject_object_count_defaults = function(object_count_opts)
+    for k, v in pairs(object_count_opts) do
+        if M.default_count_opts[k] then
+            if not v.icon then
+                v.icon = M.default_count_opts[k].icon
+            end
+            if not v.count_method then
+                v.count_method = M.default_count_opts[k].count_method
+            else -- See if any subparts are needed
+                -- Use tbl_extend here, prioritizing user definitions
+                v.count_method = vim.tbl_extend('force', M.default_count_opts[k].count_method, v.count_method)
+            end
+        end
+    end
+    return object_count_opts
+end
+
 local count_objects = function(lines)
-    local object_count_opts = config.foldtext.object_count_opts()
+    local object_count_opts = inject_object_count_defaults(config.foldtext.object_count_opts())
     -- Organize the object counts by tally method
     local tally_methods = {
         blocks = {},