Auto merge of #41055 - Archytaus:compile-fail/const-match-pattern-arm, r=arielb1

Fixed ICEs with pattern matching in const expression

Fixed 2 ICEs with when pattern matching inside a constant expression.

Both of these ICEs now resolve to an appropriate compiler error.

1. ICE was caused by a compiler bug to implement discriminant const qualify.

    I removed this intentionally thrown bug and changed it to a FIXME as the unimplemented expression type is handled as a compiler error elsewhere.

2. ICE was caused during a drop check when checking if a variable lifetime outlives the current scope if there was no parent scope .

    I've changed it to stop checking if there is no parent scope for the current scope. It is valid syntax for a const variable to be assigned a match expression with no enclosing scope.

    The ICE seemed to mainly be used as a defensive check for bugs elsewhere.

Fixes #38199.
Fixes #31577.
Fixes #29093.
Fixes #40012.