Add search terms in random and expression categories (#7736)

# Description

Refers to: [5093](https://github.com/nushell/nushell/issues/5093)

# Tests

- [x] `cargo fmt --all -- --check` to check standard code formatting
(`cargo fmt --all` applies these changes)
- [x] `cargo clippy --workspace -- -D warnings -D clippy::unwrap_used -A
clippy::needless_collect` to check that you're using the standard code
style
- [x]  `cargo test --workspace` to check that all tests pass

crates/nu-command/src/dataframe/expressions/alias.rs

@@ -59,6 +59,10 @@ impl Command for ExprAlias {
         }]
     }
 
+    fn search_terms(&self) -> Vec<&str> {
+        vec!["aka", "abbr", "otherwise"]
+    }
+
     fn run(
         &self,
         engine_state: &EngineState,

crates/nu-command/src/dataframe/expressions/arg_where.rs

@@ -43,6 +43,10 @@ impl Command for ExprArgWhere {
         }]
     }
 
+    fn search_terms(&self) -> Vec<&str> {
+        vec!["condition", "match", "if"]
+    }
+
     fn run(
         &self,
         engine_state: &EngineState,

crates/nu-command/src/dataframe/expressions/as_nu.rs

@@ -37,6 +37,10 @@ impl Command for ExprAsNu {
         }]
     }
 
+    fn search_terms(&self) -> Vec<&str> {
+        vec!["convert", "conversion"]
+    }
+
     fn run(
         &self,
         _engine_state: &EngineState,

crates/nu-command/src/dataframe/expressions/col.rs

@@ -43,6 +43,10 @@ impl Command for ExprCol {
         }]
     }
 
+    fn search_terms(&self) -> Vec<&str> {
+        vec!["create"]
+    }
+
     fn run(
         &self,
         engine_state: &EngineState,

crates/nu-command/src/dataframe/expressions/concat_str.rs

@@ -69,6 +69,10 @@ impl Command for ExprConcatStr {
         }]
     }
 
+    fn search_terms(&self) -> Vec<&str> {
+        vec!["join", "connect", "update"]
+    }
+
     fn run(
         &self,
         engine_state: &EngineState,

crates/nu-command/src/dataframe/expressions/is_in.rs

@@ -65,6 +65,10 @@ impl Command for ExprIsIn {
         }]
     }
 
+    fn search_terms(&self) -> Vec<&str> {
+        vec!["check", "contained", "is-contain", "match"]
+    }
+
     fn run(
         &self,
         engine_state: &EngineState,

crates/nu-command/src/dataframe/expressions/lit.rs

@@ -42,6 +42,10 @@ impl Command for ExprLit {
         }]
     }
 
+    fn search_terms(&self) -> Vec<&str> {
+        vec!["string", "literal", "expression"]
+    }
+
     fn run(
         &self,
         engine_state: &EngineState,

crates/nu-command/src/dataframe/expressions/otherwise.rs

@@ -79,6 +79,10 @@ impl Command for ExprOtherwise {
         ]
     }
 
+    fn search_terms(&self) -> Vec<&str> {
+        vec!["condition", "else"]
+    }
+
     fn run(
         &self,
         engine_state: &EngineState,

crates/nu-command/src/dataframe/expressions/quantile.rs

@@ -55,6 +55,10 @@ impl Command for ExprQuantile {
         }]
     }
 
+    fn search_terms(&self) -> Vec<&str> {
+        vec!["statistics", "percentile", "distribution"]
+    }
+
     fn run(
         &self,
         engine_state: &EngineState,

crates/nu-command/src/dataframe/expressions/when.rs

@@ -85,6 +85,10 @@ impl Command for ExprWhen {
         ]
     }
 
+    fn search_terms(&self) -> Vec<&str> {
+        vec!["condition", "match", "if", "else"]
+    }
+
     fn run(
         &self,
         engine_state: &EngineState,