feat(treesitter): upstream foldexpr from nvim-treesitter

runtime/queries/c/folds.scm

@@ -0,0 +1,19 @@
+[
+ (for_statement)
+ (if_statement)
+ (while_statement)
+ (switch_statement)
+ (case_statement)
+ (function_definition)
+ (struct_specifier)
+ (enum_specifier)
+ (comment)
+ (preproc_if)
+ (preproc_elif)
+ (preproc_else)
+ (preproc_ifdef)
+ (initializer_list)
+] @fold
+
+ (compound_statement
+  (compound_statement) @fold)