Fix improperly escaped strings in stor update (#14921)

# Description

Fixes #14909 with the same technique used in #12820 for `stor insert`.
Single quotes (and others) now work properly in strings passed to `stor
update`. Also did some minor refactoring on `stor insert` so it matches
the changes in `stor update`.

# User-Facing Changes

Bug-fix.

# Tests + Formatting

Test added for this scenario.

- 🟢 `toolkit fmt`
- 🟢 `toolkit clippy`
- 🟢 `toolkit test`
- 🟢 `toolkit test stdlib`

# After Submitting

N/A

crates/nu-command/tests/commands/mod.rs

@@ -105,6 +105,7 @@ mod sort_by;
 mod source_env;
 mod split_column;
 mod split_row;
+mod stor;
 mod str_;
 mod table;
 mod take;