[pick #18710][Disassembler] Fix string contraction logic (#18713)

## Description

Always pick whole UTF8 characters.

## Test plan

Tested against a package containing a UTF8 constant.

---

## Release notes

Check each box that your changes affect. If none of the boxes relate to
your changes, release notes aren't required.

For each box you select, include information after the relevant heading
that describes the impact of your changes that a user might notice and
any actions they must take to implement updates.

- [ ] Protocol:
- [x] Nodes (Validators and Full nodes): Bugfix for fetching package
information over JSONRPC from fullnodes, where a package containing UTF8
string constants could fail to disassemble.
- [ ] Indexer:
- [ ] JSON-RPC:
- [ ] GraphQL:
- [ ] CLI:
- [ ] Rust SDK:
- [ ] REST API:

external-crates/move/crates/move-disassembler/src/disassembler.rs

@@ -452,7 +452,9 @@ impl<'a> Disassembler<'a> {
         if s.len() <= PREVIEW_LEN + 2 {
             s.to_string()
         } else {
-            format!("{}..", &s[..PREVIEW_LEN])
+            let mut preview: String = s.chars().take(PREVIEW_LEN).collect();
+            preview.push_str("..");
+            preview
         }
     }