Fix grammar for RangePatternBound regarding literals

The compiler, in parsing, accepts many more kinds of literals in the
bound of a range pattern than what we had documented, and as with
`PatternWithoutRange`, the parser allows each of these literals to be
prefixed with `-`.  E.g.

```rust
#[cfg(any())]
match () {
    ..-true | ..-false => (),
    ..-'x' => (),
    ..-b'x' => (),
    ..-"x" => (),
    ..-r"x" => (),
    ..-br"x" => (),
    ..-c"x" => (),
    ..-cr"x" => (),
    ..-1 => (),
    ..-1.1 => (),
}
```

Let's fix this by adjusting the `RangePatternBound` production to use
`LiteralPattern`.  In a separate PR, we've adjusted `LiteralPattern`
to allow for a minus sign ahead of all literal expressions.

To help the reader, let's also add a note that highlights that what we
discuss later as being allowed semantically is more restrictive than
what we allow in parsing (and therefore in the grammar).

Author: traviscross

src/patterns.md

@@ -497,10 +497,7 @@ ObsoleteRangePattern ->
     RangePatternBound `...` RangePatternBound
 
 RangePatternBound ->
-      CHAR_LITERAL
-    | BYTE_LITERAL
-    | `-`? INTEGER_LITERAL
-    | `-`? FLOAT_LITERAL
+      LiteralPattern
     | PathExpression
 ```
 
@@ -553,7 +550,11 @@ A bound is written as one of:
 
 * A character, byte, integer, or float literal.
 * A `-` followed by an integer or float literal.
-* A [path]
+* A [path].
+
+> [!NOTE]
+>
+> The Rust parser, and therefore the grammar, accepts more than this for a range bound in a pattern, but these other things are rejected after parsing.
 
 r[patterns.range.constraint-bound-path]
 If a bound is written as a path, after macro resolution, the path must resolve to a constant item of the type `char`, an integer type, or a float type.