Always wait for completion resolve before applying the completion edits (#18907)

After https://github.com/rust-lang/rust-analyzer/pull/18167 and certain
people who type and complete rapidly, it turned out that we have not
waited for `completionItem/resolve` to finish before applying the
completion results.

Release Notes:

- Fixed completion items applied improperly on fast typing

crates/editor/src/test/editor_test_context.rs

@@ -13,6 +13,7 @@ use itertools::Itertools;
 use language::{Buffer, BufferSnapshot, LanguageRegistry};
 use multi_buffer::{ExcerptRange, ToPoint};
 use parking_lot::RwLock;
+use pretty_assertions::assert_eq;
 use project::{FakeFs, Project};
 use std::{
     any::TypeId,