Similar to what we do for 'throws' checking, perform argument-specific
checking for unsafe call arguments. This provides more detailed failures:
```
example.swift:18:3: warning: expression uses unsafe constructs but is not
marked with 'unsafe' [#StrictMemorySafety]
16 | x.f(a: 0, b: 17, c: nil)
17 |
18 | x.f(a: 0, b: 17, c: &i)
| | `- note: argument 'c' in call to instance
method 'f' has unsafe type 'UnsafePointer<Int>?'
| `- warning: expression uses unsafe constructs but is not marked
with 'unsafe' [#StrictMemorySafety]
19 | unsafeF()
20 | }
```
It also means that we won't complain for `nil` or `Optional.none`
arguments passed to unsafe types, which eliminates some false
positives, and won't complain about unsafe result types when there is
a call---because we'd still get complaints later about the
actually-unsafe bit, which is using those results.
Fixes rdar://149629670.
Print diagnostic groups as part of the LLVM printer in the same manner as the
Swift one does, always. Make `-print-diagnostic-groups` an inert option, since we
always print diagnostic group names with the `[#GroupName]` syntax.
As part of this, we no longer render the diagnostic group name as part
of the diagnostic *text*, instead leaving it up to the diagnostic
renderer to handle the category appropriately. Update all of the tests
that were depending on `-print-diagnostic-groups` putting it into the
text to instead use the `{{documentation-file=<file name>}}`
diagnostic verification syntax.
With the acceptance of SE-0458, allow the use of unsafe expressions, the
@safe and @unsafe attributes, and the `unsafe` effect on the for..in loop
in all Swift code.
Introduce the `-strict-memory-safety` flag detailed in the proposal to
enable strict memory safety checking. This enables a new class of
feature, an optional feature (that is *not* upcoming or experimental),
and which can be detected via `hasFeature(StrictMemorySafety)`.
When calling an explicitly-@safe function or subscript, or accessing an
explicitly-@safe property, the direct arguments to that operation can be
considered safe if they are references to local variables or are references
to types.
This brings the implementation in line with the recent adjustments to the
proposal within the review.
