Detect and fix situations when (force) unwrap is used on
a non-optional type, this helps to diagnose invalid unwraps
precisely and provide fix-its.
Resolves: [SR-8977](https://bugs.swift.org/browse/SR-8977)
Resolves: rdar://problem/45218255
If the base type is not optional, trying to unwrap it is
incorrect. Introduce a fix to make it look like base was
an optional type which leads solver to move forward
towards possible solution.
Suggest to add `()` (form a call) to correctly forward argument function
originated from `@autoclosure` parameter to function parameter itself
marked as `@autoclosure`.
Let's keep track of type mismatch between type deduced
for the body of the closure vs. what is requested
contextually, it makes it much easier to diagnose
problems like:
```swift
func foo(_: () -> Int) {}
foo { "hello" }
```
Because we can pin-point problematic area of the source
when the rest of the system is consistent.
Resolves: rdar://problem/40537960
Since `ConstraintFix` references `ConstraintSystem` directly now,
we can get `SourceManager` from `ASTContext` associated with that
`ConstraintSystem` instead of passing it in every time.
There is no longer any reason to attach solution to `ConstraintFix`
because solution applied to the constraint system before any of the
related fixes are diagnosed, so instead let's attach `ConstraintSystem`
to `ConstraintFix` directly, because it would have all of the required
information.
Since constraint fix life span is tightly coupled with particular
constraint system, it makes sense to allocate fixes using the same
allocator as used for constraints.
A fix is related to one of the constraints through its locator,
and contains information required to "fix" a failure associated with
given constraint, each of the fixes also includes diagnostic.
