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/char_.rs

@@ -165,9 +165,9 @@ impl Command for Char {
             .optional(
                 "character",
                 SyntaxShape::Any,
-                "the name of the character to output",
+                "The name of the character to output.",
             )
-            .rest("rest", SyntaxShape::Any, "multiple Unicode bytes")
+            .rest("rest", SyntaxShape::Any, "Multiple Unicode bytes.")
             .switch("list", "List all supported character names", Some('l'))
             .switch("unicode", "Unicode string i.e. 1f378", Some('u'))
             .switch("integer", "Create a codepoint from an integer", Some('i'))