fix: Define DecimalLiteral in DSL v2 using the DSL v1 rules

Otherwise, the following rule:

```rust
// An integer (without a dot or a fraction) is enabled in all versions:
TokenDefinition(
    scanner = TrailingContext(
        scanner = Sequence([
            Fragment(DecimalDigits),
            Optional(Fragment(DecimalExponent))
        ]),
        not_followed_by = Fragment(IdentifierStart)
    )
),
```

was a catch-all rule that could successfully lex "1.2" as "1" in all versions.

Instead, this mimicks the following version from the DSL v1:
```rust
scanner DecimalLiteral = (
        (
            (
                { removed in "0.5.0"    (DecimalDigits (("." (DecimalDigits ?) ) ?)) } |
                { introduced in "0.5.0" (DecimalDigits (("." DecimalDigits     ) ?)) } |
                ('.' DecimalDigits)
            )
            (DecimalExponent ?)
        ) not followed by IdentifierStart
    ) ;
```

crates/solidity/inputs/language/src/definition.rs

@@ -3671,44 +3671,44 @@ codegen_language_macros::compile!(Language(
                         Token(
                             name = DecimalLiteral,
                             definitions = [
-                                // An integer (without a dot or a fraction) is enabled in all versions:
-                                TokenDefinition(
-                                    scanner = TrailingContext(
-                                        scanner = Sequence([
-                                            Fragment(DecimalDigits),
-                                            Optional(Fragment(DecimalExponent))
-                                        ]),
-                                        not_followed_by = Fragment(IdentifierStart)
-                                    )
-                                ),
-                                // An integer and a dot (without a fraction) is disabled in "0.5.0"
+                                // An integer, optionally with a dot that may not be followed by a fraction, is disabled in "0.5.0":
                                 TokenDefinition(
                                     enabled = Till("0.5.0"),
                                     scanner = TrailingContext(
                                         scanner = Sequence([
-                                            Fragment(DecimalDigits),
-                                            Atom("."),
+                                            Sequence([
+                                                Fragment(DecimalDigits),
+                                                Optional(Sequence([
+                                                    Atom("."),
+                                                    Optional(Fragment(DecimalDigits))
+                                                ]))
+                                            ]),
                                             Optional(Fragment(DecimalExponent))
                                         ]),
                                         not_followed_by = Fragment(IdentifierStart)
                                     )
                                 ),
-                                // A dot and a fraction (without an integer) is enabled in all versions:
+                                // An integer, optionally with dot that is always followed by a fraction, is enabled in "0.5.0":
                                 TokenDefinition(
+                                    enabled = From("0.5.0"),
                                     scanner = TrailingContext(
                                         scanner = Sequence([
-                                            Atom("."),
-                                            Fragment(DecimalDigits),
+                                            Sequence([
+                                                Fragment(DecimalDigits),
+                                                Optional(Sequence([
+                                                    Atom("."),
+                                                    Fragment(DecimalDigits)
+                                                ]))
+                                            ]),
                                             Optional(Fragment(DecimalExponent))
                                         ]),
                                         not_followed_by = Fragment(IdentifierStart)
                                     )
                                 ),
-                                // An integer, a dot, and a fraction is enabled in all versions:
+                                // A dot and a fraction (without an integer) is enabled in all versions:
                                 TokenDefinition(
                                     scanner = TrailingContext(
                                         scanner = Sequence([
-                                            Fragment(DecimalDigits),
                                             Atom("."),
                                             Fragment(DecimalDigits),
                                             Optional(Fragment(DecimalExponent))