Make string related commands parse-time evaluatable (#13032)

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Related meta-issue: #10239.

# Description
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This PR will modify some `str`-related commands so that they can be
evaluated at parse time.

See the following list for those implemented by this pr.

# User-Facing Changes
<!-- List of all changes that impact the user experience here. This
helps us keep track of breaking changes. -->

Available now:
- `str` subcommands
  - `trim`
  - `contains`
  - `distance`
  - `ends-with`
  - `expand`
  - `index-of`
  - `join`
  - `replace`
  - `reverse`
  - `starts-with`
  - `stats`
  - `substring`
  - `capitalize`
  - `downcase`
  - `upcase`
- `split` subcommands
  - `chars`
  - `column`
  - `list`
  - `row`
  - `words`
- `format` subcommands
  - `date`
  - `duration`
  - `filesize`
- string related commands
  - `parse`
  - `detect columns`
  - `encode` & `decode`

# Tests + Formatting
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- `cargo run -- -c "use toolkit.nu; toolkit test stdlib"` to run the
tests for the standard library

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Unresolved questions:
- [ ] Is there any routine of testing const expressions? I haven't found
any yet.
- [ ] Is const expressions required to behave just like there non-const
version, like what rust promises?

# After Submitting
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Unresolved questions:
- [ ] Do const commands need special marks in the docs?

crates/nu-command/src/strings/str_/substring.rs

@@ -1,10 +1,10 @@
-use crate::grapheme_flags;
+use crate::{grapheme_flags, grapheme_flags_const};
 use nu_cmd_base::{
     input_handler::{operate, CmdArgument},
     util,
 };
 use nu_engine::command_prelude::*;
-use nu_protocol::Range;
+use nu_protocol::{engine::StateWorkingSet, Range};
 use std::cmp::Ordering;
 use unicode_segmentation::UnicodeSegmentation;
 
@@ -77,6 +77,10 @@ impl Command for SubCommand {
         vec!["slice"]
     }
 
+    fn is_const(&self) -> bool {
+        true
+    }
+
     fn run(
         &self,
         engine_state: &EngineState,
@@ -103,6 +107,37 @@ impl Command for SubCommand {
         operate(action, args, input, call.head, engine_state.ctrlc.clone())
     }
 
+    fn run_const(
+        &self,
+        working_set: &StateWorkingSet,
+        call: &Call,
+        input: PipelineData,
+    ) -> Result<PipelineData, ShellError> {
+        let range: Range = call.req_const(working_set, 0)?;
+
+        let indexes = match util::process_range(&range) {
+            Ok(idxs) => idxs.into(),
+            Err(processing_error) => {
+                return Err(processing_error("could not perform substring", call.head))
+            }
+        };
+
+        let cell_paths: Vec<CellPath> = call.rest_const(working_set, 1)?;
+        let cell_paths = (!cell_paths.is_empty()).then_some(cell_paths);
+        let args = Arguments {
+            indexes,
+            cell_paths,
+            graphemes: grapheme_flags_const(working_set, call)?,
+        };
+        operate(
+            action,
+            args,
+            input,
+            call.head,
+            working_set.permanent().ctrlc.clone(),
+        )
+    }
+
     fn examples(&self) -> Vec<Example> {
         vec![
             Example {