Ensure that command usage starts uppercase and ends period (#11278)

# Description

This repeats #8268 to make all command usage strings start with an
uppercase letter and end with a period per #5056

Adds a test to ensure that commands won't regress

Part of #5066

# User-Facing Changes

Command usage is now consistent

# Tests + Formatting

- 🟢 `toolkit fmt`
- 🟢 `toolkit clippy`
- 🟢 `toolkit test`
- 🟢 `toolkit test stdlib`

# After Submitting

Automatic documentation updates

crates/nu-command/src/platform/input/input_listen.rs

@@ -49,7 +49,7 @@ impl Command for InputListen {
     }
 
     fn usage(&self) -> &str {
-        "Listen for user interface event"
+        "Listen for user interface event."
     }
 
     fn extra_usage(&self) -> &str {

crates/nu-command/src/platform/is_terminal.rs

@@ -23,7 +23,7 @@ impl Command for IsTerminal {
     }
 
     fn usage(&self) -> &str {
-        "Check if stdin, stdout, or stderr is a terminal"
+        "Check if stdin, stdout, or stderr is a terminal."
     }
 
     fn examples(&self) -> Vec<Example> {