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/strings/format/date.rs

@@ -32,7 +32,7 @@ impl Command for FormatDate {
             .optional(
                 "format string",
                 SyntaxShape::String,
-                "the desired format date",
+                "The desired format date.",
             )
             .category(Category::Date)
     }

crates/nu-command/src/strings/format/duration.rs

@@ -40,12 +40,12 @@ impl Command for FormatDuration {
             .required(
                 "format value",
                 SyntaxShape::String,
-                "the unit in which to display the duration",
+                "The unit in which to display the duration.",
             )
             .rest(
                 "rest",
                 SyntaxShape::CellPath,
-                "For a data structure input, format duration at the given cell paths",
+                "For a data structure input, format duration at the given cell paths.",
             )
             .category(Category::Strings)
     }

crates/nu-command/src/strings/format/filesize.rs

@@ -37,12 +37,12 @@ impl Command for FormatFilesize {
             .required(
                 "format value",
                 SyntaxShape::String,
-                "the format into which convert the file sizes",
+                "The format into which convert the file sizes.",
             )
             .rest(
                 "rest",
                 SyntaxShape::CellPath,
-                "For a data structure input, format filesizes at the given cell paths",
+                "For a data structure input, format filesizes at the given cell paths.",
             )
             .category(Category::Strings)
     }