Implement postfix adjustment hints

I'd say "First stab at implementing..." but I've been working on this
for a month already lol

crates/ide/src/static_index.rs

@@ -115,6 +115,7 @@ impl StaticIndex<'_> {
                     closure_return_type_hints: crate::ClosureReturnTypeHints::WithBlock,
                     lifetime_elision_hints: crate::LifetimeElisionHints::Never,
                     adjustment_hints: crate::AdjustmentHints::Never,
+                    adjustment_hints_postfix: false,
                     adjustment_hints_hide_outside_unsafe: false,
                     hide_named_constructor_hints: false,
                     hide_closure_initialization_hints: false,