A new subcommand to str, str-expand. (#9290)

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Description can be found [here:
https://github.com/nushell/nushell/discussions/9277#discussioncomment-5997793](https://github.com/nushell/nushell/discussions/9277#discussioncomment-5997793)

# User-Facing Changes

Again, examples can be found in the discussion #9277

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---------

Co-authored-by: Darren Schroeder <343840+fdncred@users.noreply.github.com>

crates/nu-command/src/default_context.rs

@@ -195,6 +195,7 @@ pub fn add_shell_command_context(mut engine_state: EngineState) -> EngineState {
             StrDistance,
             StrDowncase,
             StrEndswith,
+            StrExpand,
             StrJoin,
             StrReplace,
             StrIndexOf,