Detect expiry of loans to trivially destructed types

[usx95]

#include <string_view>

class S {
    std::string_view a, b;
};

void foo() {
    S* ptr;
    {
        S s;
        ptr = &s;
    }
    (void)ptr;
}

We do not have destructor calls and therefore no expiry facts for the loans created.

CFG and LifetimeFacts

[B2 (ENTRY)]
   Succs (1): B1
 [B1]
   1: S *ptr;
   2:  (CXXConstructExpr, S)
   3: S s;
   4: s
   5: &[B1.4]
   6: ptr
   7: [B1.6] = [B1.5]
   8: ptr
   9: (void)[B1.8] (CStyleCastExpr, ToVoid, void)
   Preds (1): B2
   Succs (1): B0
 [B0 (EXIT)]
   Preds (1): B1

==========================================
       Lifetime Analysis Facts:
==========================================
Function: foo
  Block B2:
  End of Block
  Block B1:
    Issue (0 (Path: s), ToOrigin: 0 (Expr: DeclRefExpr))
    OriginFlow (Dest: 1 (Expr: UnaryOperator), Src: 0 (Expr: DeclRefExpr))
    Use (2 (Decl: ptr), Write)
    OriginFlow (Dest: 2 (Decl: ptr), Src: 1 (Expr: UnaryOperator))
    Use (2 (Decl: ptr), Read)
  End of Block
  Block B0:
  End of Block
Compiler returned: 0

We can use AddLifetime to make CFG add lifetime related events where destructor calls are not in the CFG.

[llvmbot]

@llvm/issue-subscribers-clang-temporal-safety

Author: Utkarsh Saxena (usx95)

```cpp #include <string_view>

class S {
std::string_view a, b;
};

void foo() {
S* ptr;
{
S s;
ptr = &s;
}
(void)ptr;
}

We do not have destructor calls and therefore no expiry facts for the loans created.

CFG and LifetimeFacts

[B2 (ENTRY)]
Succs (1): B1
[B1]
1: S *ptr;
2: (CXXConstructExpr, S)
3: S s;
4: s
5: &[B1.4]
6: ptr
7: [B1.6] = [B1.5]
8: ptr
9: (void)[B1.8] (CStyleCastExpr, ToVoid, void)
Preds (1): B2
Succs (1): B0
[B0 (EXIT)]
Preds (1): B1

==========================================
Lifetime Analysis Facts:

Function: foo
Block B2:
End of Block
Block B1:
Issue (0 (Path: s), ToOrigin: 0 (Expr: DeclRefExpr))
OriginFlow (Dest: 1 (Expr: UnaryOperator), Src: 0 (Expr: DeclRefExpr))
Use (2 (Decl: ptr), Write)
OriginFlow (Dest: 2 (Decl: ptr), Src: 1 (Expr: UnaryOperator))
Use (2 (Decl: ptr), Read)
End of Block
Block B0:
End of Block
Compiler returned: 0

We can use `AddLifetime` to make CFG add lifetime related events where destructor calls are not in the CFG.
</details>