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"
```
