Enforce required, optional, and rest positional arguments start with an uppercase and end with a period. (#11285)

# Description

This updates all the positional arguments (except with
`--features=dataframe` or `--features=extra`) to start with an uppercase
letter and end with a period.

Part of #5066, specifically [this
comment](/nushell/nushell/issues/5066#issuecomment-1421528910)

Some arguments had example data removed from them because it also
appears in the examples.

There are other inconsistencies in positional arguments I noticed while
making the tests pass which I will bring up in #5066.

# User-Facing Changes

Positional arguments are now consistent

# Tests + Formatting

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

# After Submitting

Automatic documentation updates

crates/nu-lsp/src/notification.rs

@@ -121,7 +121,7 @@ mod tests {
             serde_json::json!({
                 "contents": {
                     "kind": "markdown",
-                    "value": "\n### Signature\n```\n  let {flags} <var_name> <initial_value>\n```\n\n### Parameters\n\n  `var_name: any` - variable name\n\n  `initial_value: any` - equals sign followed by value\n\n\n### Flags\n\n  `-h`, `--help` - Display the help message for this command\n\n### Input/output\n\n```\n any | nothing\n\n```\n### Usage\n  Create a variable and give it a value.\n\n### Extra usage:\n  This command is a parser keyword. For details, check:\n  https://www.nushell.sh/book/thinking_in_nu.html\n### Example(s)\n  Set a variable to a value\n```\n  let x = 10\n```\n  Set a variable to the result of an expression\n```\n  let x = 10 + 100\n```\n  Set a variable based on the condition\n```\n  let x = if false { -1 } else { 1 }\n```\n"
+                    "value": "\n### Signature\n```\n  let {flags} <var_name> <initial_value>\n```\n\n### Parameters\n\n  `var_name: any` - Variable name.\n\n  `initial_value: any` - Equals sign followed by value.\n\n\n### Flags\n\n  `-h`, `--help` - Display the help message for this command\n\n### Input/output\n\n```\n any | nothing\n\n```\n### Usage\n  Create a variable and give it a value.\n\n### Extra usage:\n  This command is a parser keyword. For details, check:\n  https://www.nushell.sh/book/thinking_in_nu.html\n### Example(s)\n  Set a variable to a value\n```\n  let x = 10\n```\n  Set a variable to the result of an expression\n```\n  let x = 10 + 100\n```\n  Set a variable based on the condition\n```\n  let x = if false { -1 } else { 1 }\n```\n"
                 }
             })
         );