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-command/src/misc/source.rs

@@ -18,7 +18,7 @@ impl Command for Source {
             .required(
                 "filename",
                 SyntaxShape::Filepath,
-                "the filepath to the script file to source",
+                "The filepath to the script file to source.",
             )
             .category(Category::Core)
     }

crates/nu-command/src/misc/tutor.rs

@@ -22,7 +22,7 @@ impl Command for Tutor {
             .optional(
                 "search",
                 SyntaxShape::String,
-                "item to search for, or 'list' to list available tutorials",
+                "Item to search for, or 'list' to list available tutorials.",
             )
             .named(
                 "find",