Auto merge of #7346 - lengyijun:redundant_clone_5707, r=oli-obk

fix 5707

changelog: ``[`redundant_clone`]``, fix #5707

# Root problem of #5707 :
```
&2:&mut HashMap = &mut _4;
&3:&str = & _5;
_1 = HashMap::insert(move _2,move _3, _);
```

generate PossibleBorrower(_2,_1) and PossibleBorrower(_3,_1).

However, it misses PossibleBorrower(_3,_2).

# My solution to #5707 :

When meet a function call, we should:
1. build PossibleBorrower between borrow parameters and return value (currently)
2. build PossibleBorrower between immutable borrow parameters and mutable borrow parameters (*add*)
3. build PossibleBorrower inside mutable borrow parameters (*add*)

For example:
```
_2: &mut _22;
_3: &mut _;
_4: & _;
_5: & _;
_1 = call(move _2, move _3, move _4, move _5);
```
we need to build
1. return value with parameter(current implementataion)
 PossibleBorrower(_2,_1)
 PossibleBorrower(_3,_1)
 PossibleBorrower(_4,_1)
 PossibleBorrower(_5,_1)

2. between mutable borrow and immutable borrow
PossibleBorrower(_4,_2)
PossibleBorrower(_5,_2)
PossibleBorrower(_4,_3)
PossibleBorrower(_5,_3)

3. between mutable borrow and mutable borrow
PossibleBorrower(_3,_2)
PossibleBorrower(_2,_3)

  But that's not enough.
 Modification to _2 actually apply to _22.
  So I write a `PossibleBorrowed` visitor, which tracks (borrower => possible borrowed) relation.
  For example (_2 => _22).
  However, a lot of problems exist here.

## Known Problems:
  1. not sure all `&mut`'s origin are collected.
  I'm not sure how to deal with `&mut` when meet a function call, so I didn't do it currently.
  Also, my implement is not flow sensitive, so it's not accurate.

```
foo(_2:&mut _, _3: &_)
```
This pr doesn't count _3 as origin of _2.

 2. introduce false negative
`foo(_2, _3)` will  emit PossibleBorrower(_3,_2) in this pr, but _3 and _2 may not have relation.
Clippy may feel that _3 is still in use because of _2, but actually, _3 is on longer needed and can be moved.

## Insight
  The key problem is determine where every `&mut` come from accurately.
  I think Polonius is an elegant solution to it. Polonius is flow sensitive and accurate.
  But I'm uncertain about whether we can import Polonius in rust-clippy currently.
  This pr actually is part of Polonius' functionality, I think.

# TODO
1. `cargo test` can't pass yet due to similar variable name

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