Make {.requiresInit.} to work for distinct types (#15869)

Make `requiresInit` pragma to work for distinct types in addition to
objects. Tagging of distinct types with `requiresInit` pragma was
already supported, but its impact wasn't applied. Now its behavior when
applied on distinct types is as follows.

Given the following distinct type definitions:

  ```nim
  type
    DistinctObject {.requiresInit, borrow: `.`.} = distinct MyObject
    DistinctString {.requiresInit.} = distinct string
  ```

The following code blocks will fail to compile:

  ```nim
  var foo: DistinctFoo
  foo.x = "test"
  doAssert foo.x == "test"
  ```

  ```nim
  var s: DistinctString
  s = "test"
  doAssert s == "test"
  ```

But these ones will compile successfully:

  ```nim
  let foo = DistinctFoo(Foo(x: "test"))
  doAssert foo.x == "test"
  ```

  ```nim
  let s = "test"
  doAssert s == "test"
  ```

compiler/semstmts.nim

@@ -611,7 +611,8 @@ proc semVarOrLet(c: PContext, n: PNode, symkind: TSymKind): PNode =
       if def.kind == nkEmpty:
         let actualType = v.typ.skipTypes({tyGenericInst, tyAlias,
                                           tyUserTypeClassInst})
-        if actualType.kind == tyObject and actualType.requiresInit:
+        if actualType.kind in {tyObject, tyDistinct} and
+           actualType.requiresInit:
           defaultConstructionError(c, v.typ, v.info)
         else:
           checkNilable(c, v)