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.

lib/pure/collections/tableimpl.nim

@@ -121,12 +121,12 @@ template ctAnd(a, b): bool =
   else: false
 
 template initImpl(result: typed, size: int) =
+  let correctSize = slotsNeeded(size)
   when ctAnd(declared(SharedTable), type(result) is SharedTable):
-    init(result, size)
+    init(result, correctSize)
   else:
-    assert isPowerOfTwo(size)
     result.counter = 0
-    newSeq(result.data, size)
+    newSeq(result.data, correctSize)
     when compiles(result.first):
       result.first = -1
       result.last = -1