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/generators/generate.rs

@@ -24,11 +24,11 @@ impl Command for Generate {
                     Type::List(Box::new(Type::Any)),
                 ),
             ])
-            .required("initial", SyntaxShape::Any, "initial value")
+            .required("initial", SyntaxShape::Any, "Initial value.")
             .required(
                 "closure",
                 SyntaxShape::Closure(Some(vec![SyntaxShape::Any])),
-                "generator function",
+                "Generator function.",
             )
             .allow_variants_without_examples(true)
             .category(Category::Generators)

crates/nu-command/src/generators/seq.rs

@@ -17,7 +17,7 @@ impl Command for Seq {
     fn signature(&self) -> Signature {
         Signature::build("seq")
             .input_output_types(vec![(Type::Nothing, Type::List(Box::new(Type::Number)))])
-            .rest("rest", SyntaxShape::Number, "sequence values")
+            .rest("rest", SyntaxShape::Number, "Sequence values.")
             .category(Category::Generators)
     }
 

crates/nu-command/src/generators/seq_char.rs

@@ -23,12 +23,12 @@ impl Command for SeqChar {
             .required(
                 "start",
                 SyntaxShape::String,
-                "start of character sequence (inclusive)",
+                "Start of character sequence (inclusive).",
             )
             .required(
                 "end",
                 SyntaxShape::String,
-                "end of character sequence (inclusive)",
+                "End of character sequence (inclusive).",
             )
             .category(Category::Generators)
     }