New lint no_effect_replace

[guerinoni]

Closes #1595

Signed-off-by: Federico Guerinoni [email protected]

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changelog:
Add no_effect_replace lint.

[rust-highfive]

r? @flip1995

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[bors]

☔ The latest upstream changes (presumably #8727) made this pull request unmergeable. Please resolve the merge conflicts.

[xFrednet]

r? @dswij 🙃

[matthiaskrgr]

Might be nice to also have tests where we do something like let x=...; foo.replace(x,x); and foo.replace(x.f(),x.f()) where x is a fn f(&mut self)

[guerinoni]

Moved to #8754 because changing PC I messed up something :)