Auto merge of #69676 - ecstatic-morse:fix-enum-discr-effect, r=oli-obk
Auto merge of #69676 - ecstatic-morse:fix-enum-discr-effect, r=oli-obk

Pass correct place to `discriminant_switch_effect`

PR #69562, which fixed a bug that was causing clippy to ICE, mistakenly passed the place holding the *result* of `Rvalue::Discriminant` instead of the place holding its *operand* to `apply_discriminant_switch_effect` as the enum place. As a result, no effect was applied at all, and we lost the perf benefits from marking inactive enum variants as uninitialized.

**edit:** The regression test has been split into #69744.

r? @oli-obk

graydon/rust,graydon/rust,aidancully/rust,graydon/rust,aidancully/rust,graydon/rust,aidancully/rust,aidancully/rust,aidancully/rust,graydon/rust,aidancully/rust,graydon/rust