ADA: fix folding on "null record" ; add digit separator, based numeral and keywords

- fix folding on `null record`

```ada
type Car is record -- beginRegion=RecordRegion
  -- .....
end record -- endRegion=RecordRegion
type Null_Record is null record;
-- Before                ~~~~~~ beginRegion=RecordRegion
-- After                 ~~~~~~ no region
```

- new highlight: Base, Exponent

```ada
   3#011201#e3
-- ^ Base
--   ^ Decimal
--         ^ Base
--          ^ Exponent

   3#0112401#e3
-- ^ Base
--   ^ Decimal
--       ^ Normal Text (4 is not valid in base 3)
```

BUG: 426377