CodeMod: future-then-continuation-lvalue-ref
CodeMod: future-then-continuation-lvalue-ref

Summary:
CodeMod: `future-then-continuation-lvalue-ref`.

```
buck run mode/opt foundation/clangr:clangr_coordinator -- run foundation/clang/codemods:future-then-continuation-lvalue-ref --dev -p 7 --num-workers=200
```

There is no need to support continuations taking non-const lvalue-ref params; callers can get exactly the same semantics with non-const rvalue-ref params instead. Thsi codemod preserves semantics. Many of these cases could do just as well taking by value, but this codemod preserves semantics.

Reviewed By: Orvid

Differential Revision: D8166008

fbshipit-source-id: 84b635cccce24b6485ffb5b24b98f10422b9a517

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