Function lower_expr_while_let 

pub fn lower_expr_while_let<'db>(
    ctx: &mut LoweringContext<'db, '_>,
    builder: &mut BlockBuilder<'db>,
    loop_expr: &ExprWhile<'db>,
    matched_expr: ExprId,
    patterns: &[PatternId],
    loop_expr_id: ExprId,
    loop_stable_ptr: SyntaxStablePtrId<'db>,
) -> LoweringResult<'db, LoweredExpr<'db>>

Lowers an expression of type if where the condition is of type semantic::Condition::Let.