Test command names and search terms for redundancy (#6380)

* Test commands for proper names and search terms

Assert that the `Command.name()` is equal to `Signature.name`

Check that search terms are not just substrings of the command name as
they would not help finding the command.

* Clean up search terms

Remove redundant terms that just replicate the command name.
Try to eliminate substring between search terms, clean up where
necessary.

crates/nu-command/src/math/avg.rs

@@ -21,7 +21,7 @@ impl Command for SubCommand {
     }
 
     fn search_terms(&self) -> Vec<&str> {
-        vec!["average", "mean"]
+        vec!["average", "mean", "statistics"]
     }
 
     fn run(

crates/nu-command/src/math/ceil.rs

@@ -19,7 +19,7 @@ impl Command for SubCommand {
     }
 
     fn search_terms(&self) -> Vec<&str> {
-        vec!["ceiling"]
+        vec!["ceiling", "round up", "rounding", "integer"]
     }
 
     fn run(

crates/nu-command/src/math/floor.rs

@@ -19,7 +19,7 @@ impl Command for SubCommand {
     }
 
     fn search_terms(&self) -> Vec<&str> {
-        vec!["floor"]
+        vec!["round down", "rounding", "integer"]
     }
 
     fn run(

crates/nu-command/src/math/median.rs

@@ -23,7 +23,7 @@ impl Command for SubCommand {
     }
 
     fn search_terms(&self) -> Vec<&str> {
-        vec!["middle", "median"]
+        vec!["middle", "statistics"]
     }
 
     fn run(

crates/nu-command/src/math/stddev.rs

@@ -23,7 +23,14 @@ impl Command for SubCommand {
     }
 
     fn search_terms(&self) -> Vec<&str> {
-        vec!["SD", "standard", "deviation", "dispersion", "variation"]
+        vec![
+            "SD",
+            "standard",
+            "deviation",
+            "dispersion",
+            "variation",
+            "statistics",
+        ]
     }
 
     fn run(

crates/nu-command/src/math/variance.rs

@@ -22,7 +22,7 @@ impl Command for SubCommand {
     }
 
     fn search_terms(&self) -> Vec<&str> {
-        vec!["deviation", "dispersion", "variance", "variation"]
+        vec!["deviation", "dispersion", "variation", "statistics"]
     }
 
     fn run(