Auto merge of #13517 - feniljain:fix_completions, r=Veykril

Auto merge of #13517 - feniljain:fix_completions, r=Veykril

fix: make custom expr prefix completions to understand refs

Possible fix of #7929

While reviewing the postfix completion code I saw that while calling `add_custom_postfix_completions` we were doing it under the part where reference was not taken into consideration, but as we are only adding postfix completions with `Expr` scope ( [source](https://github.com/rust-lang/rust-analyzer/blob/ba28e19b7838e3ad4223ae82d074dc3950ef1548/crates/ide-completion/src/completions/postfix.rs#L272) )

I shifted the `add_custom_postfix_completions` call to part where references are considered

I am not sure if this is the correct fix or I am understanding the problem exactly but this small move seemed to have fixed the issue :)