fix: highlighting a where command with invalid arguments can duplicate text (#16192)

- fixes #16129

# Description

## Problem
Parsing a multi span value as RowCondition always produces a RowCondition
expression that covers all the spans.

Which is problematic inside OneOf and can produce multiple expressions with
overlapping spans.
Which results in funky highlighting that duplicates text.

## Solution
Only reason for including `SyntaxShape::Closure` in the signature (#15697) was
for documentation purposes, making it clear in `help` texts that a closure can
be used as the argument.

As our current parser is shape directed, simplifying the command signature
means simplifies the parsing, so using a RowCondition on its own, and instead
making it always look like a union with `closure(any)` solves the issue without
any changes in the parser.

Also, RowCondition always accepts closure values anyway, so its textual
representation should indicate that without the need to wrap it in OneOf.

Co-authored-by: Bahex <17417311+Bahex@users.noreply.github.com>

crates/nu-cli/tests/commands/nu_highlight.rs

@@ -5,3 +5,9 @@ fn nu_highlight_not_expr() {
     let actual = nu!("'not false' | nu-highlight | ansi strip");
     assert_eq!(actual.out, "not false");
 }
+
+#[test]
+fn nu_highlight_where_row_condition() {
+    let actual = nu!("'ls | where a b 12345(' | nu-highlight | ansi strip");
+    assert_eq!(actual.out, "ls | where a b 12345(");
+}

crates/nu-command/src/filters/where_.rs

@@ -43,10 +43,7 @@ Row conditions cannot be stored in a variable. To pass a condition with a variab
             ])
             .required(
                 "condition",
-                SyntaxShape::OneOf(vec![
                 SyntaxShape::RowCondition,
-                    SyntaxShape::Closure(Some(vec![SyntaxShape::Any])),
-                ]),
                 "Filter row condition or closure.",
             )
             .allow_variants_without_examples(true)

crates/nu-protocol/src/syntax_shape.rs

@@ -239,7 +239,11 @@ impl Display for SyntaxShape {
             SyntaxShape::Duration => write!(f, "duration"),
             SyntaxShape::DateTime => write!(f, "datetime"),
             SyntaxShape::Operator => write!(f, "operator"),
-            SyntaxShape::RowCondition => write!(f, "condition"),
+            SyntaxShape::RowCondition => write!(
+                f,
+                "oneof<condition, {}>",
+                SyntaxShape::Closure(Some(vec![SyntaxShape::Any]))
+            ),
             SyntaxShape::MathExpression => write!(f, "variable"),
             SyntaxShape::VarWithOptType => write!(f, "vardecl"),
             SyntaxShape::Signature => write!(f, "signature"),