renames arrow function declaration despite keep_fnames: true

[samualtnorman]

In the source, the function is named foo and inspecting its .name gives foo.
However terser mistakenly renames the function to bar which can be observed with .name.
In the screenshot I run the before minified and after minified and you can see in the console what console.log()ing the .name gives.

the source is

let foo = () => {}
let bar = foo

console.log(bar.name)

[fabiosantoscode]

The circumstances where .name is assigned are statically analyzable (we can list the circumstances by searching for references to NamedEvaluation in the spec) so this is something that can be done.

We can for instance suppress the analysis of variable definitions that hold anonymous functions here. This approach is simple but it may have drawbacks (IE we can't inline functions into callsites now).

[fabiosantoscode]

Related: #1484