feat: add cdot combinator in grind tactic mode

[leodemoura]

This PR adds the combinator · t_1 ... t_n to the grind interactive mode. The finish? tactic now generates scripts using this combinator to conform to Mathlib coding standards. The new format is also more compact. Example:

/--
info: Try this:
  [apply] ⏎
    instantiate only [= mem_indices_of_mem, insert, = getElem_def]
    instantiate only [= getElem?_neg, = getElem?_pos]
    cases #f590
    · cases #ffdf
      · instantiate only
        instantiate only [= Array.getElem_set]
      · instantiate only
        instantiate only [size, = HashMap.mem_insert, = HashMap.getElem_insert, = Array.getElem_push]
    · instantiate only [= mem_indices_of_mem, = getElem_def]
      instantiate only [usr getElem_indices_lt]
      instantiate only [size]
      cases #ffdf
      · instantiate only [=_ WF]
        instantiate only [= getElem?_neg, = getElem?_pos, = Array.getElem_set]
        instantiate only [WF']
      · instantiate only
        instantiate only [= HashMap.mem_insert, = HashMap.getElem_insert, = Array.getElem_push]
-/
#guard_msgs in
example (m : IndexMap α β) (a a' : α) (b : β) (h : a' ∈ m.insert a b) :
    (m.insert a b)[a'] = if h' : a' == a then b else m[a'] := by
  grind => finish?