remove a condition that table size must be passed as power of 2 (#14926)

* remove a condition that table size must be passed as power of 2
* remove power-of-2 condition from sets and sharedtables
* remove power-of-2 condition from deques
* use 'correctSize' for both branches
* prettify changelog.md and fix typos
* add a changelog entry
* fix double-call of 'right-size'
* fix the same thing in sets.nim
* introduce a new internal proc `slotsNeeded`

Deprecate the public proc `rightSize`, which is not needed anymore.
Now it is an identity function, allowing the old code to work
correctly and without extra allocations.

tests/collections/ttables.nim

@@ -446,3 +446,13 @@ block: # https://github.com/nim-lang/Nim/issues/13496
   testDel(): (let t = newOrderedTable[int, int]())
   testDel(): (var t: CountTable[int])
   testDel(): (let t = newCountTable[int]())
+
+
+block testNonPowerOf2:
+  var a = initTable[int, int](7)
+  a[1] = 10
+  assert a[1] == 10
+
+  var b = initTable[int, int](9)
+  b[1] = 10
+  assert b[1] == 10