Remove Value::MatchPattern (#11356)

# Description
`Value::MatchPattern` implies that `MatchPattern`s are first-class
values. This PR removes this case, and commands must now instead use
`Expr::MatchPattern` to extract `MatchPattern`s just like how the
`match` command does using `Expr::MatchBlock`.

# User-Facing Changes
Breaking API change for `nu_protocol` crate.

crates/nu-command/src/formats/to/json.rs

@@ -127,10 +127,7 @@ pub fn value_to_json_value(v: &Value) -> Result<nu_json::Value, ShellError> {
 
         Value::List { vals, .. } => nu_json::Value::Array(json_list(vals)?),
         Value::Error { error, .. } => return Err(*error.clone()),
-        Value::Closure { .. }
-        | Value::Block { .. }
-        | Value::Range { .. }
-        | Value::MatchPattern { .. } => nu_json::Value::Null,
+        Value::Closure { .. } | Value::Block { .. } | Value::Range { .. } => nu_json::Value::Null,
         Value::Binary { val, .. } => {
             nu_json::Value::Array(val.iter().map(|x| nu_json::Value::U64(*x as u64)).collect())
         }

crates/nu-command/src/formats/to/nuon.rs

@@ -241,12 +241,6 @@ pub fn value_to_string(
                 ))
             }
         }
-        Value::MatchPattern { .. } => Err(ShellError::UnsupportedInput {
-            msg: "match patterns are currently not nuon-compatible".to_string(),
-            input: "value originates from here".into(),
-            msg_span: span,
-            input_span: v.span(),
-        }),
         Value::Nothing { .. } => Ok("null".to_string()),
         Value::Range { val, .. } => Ok(format!(
             "{}..{}{}",

crates/nu-command/src/formats/to/text.rs

@@ -148,7 +148,6 @@ fn local_into_string(value: Value, separator: &str, config: &Config) -> String {
         Value::Binary { val, .. } => format!("{val:?}"),
         Value::CellPath { val, .. } => val.to_string(),
         Value::CustomValue { val, .. } => val.value_string(),
-        Value::MatchPattern { val, .. } => format!("{:?}", val),
     }
 }
 

crates/nu-command/src/formats/to/toml.rs

@@ -94,7 +94,6 @@ fn helper(engine_state: &EngineState, v: &Value) -> Result<toml::Value, ShellErr
                 .collect::<Result<Vec<toml::Value>, ShellError>>()?,
         ),
         Value::CustomValue { .. } => toml::Value::String("<Custom Value>".to_string()),
-        Value::MatchPattern { .. } => toml::Value::String("<Match Pattern>".to_string()),
     })
 }
 

crates/nu-command/src/formats/to/yaml.rs

@@ -97,7 +97,6 @@ pub fn value_to_yaml_value(v: &Value) -> Result<serde_yaml::Value, ShellError> {
                 .collect::<Result<Vec<serde_yaml::Value>, ShellError>>()?,
         ),
         Value::CustomValue { .. } => serde_yaml::Value::Null,
-        Value::MatchPattern { .. } => serde_yaml::Value::Null,
     })
 }