fix: Define DecimalLiteral in DSL v2 using the DSL v1 rules (#643)

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
    ) ;
```

and fixed a case in
https://github.com/Xanewok/slang/tree/codegen-use-dslv2 when using parts
of the DSLv2 for the codegen but I didn't open the PR yet.

Ref #638

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

@@ -3675,7 +3675,10 @@ codegen_language_macros::compile!(Language(
                                 TokenDefinition(
                                     scanner = TrailingContext(
                                         scanner = Sequence([
-                                            Fragment(DecimalDigits),
+                                            TrailingContext(
+                                                scanner = Fragment(DecimalDigits),
+                                                not_followed_by = Atom(".")
+                                            ),
                                             Optional(Fragment(DecimalExponent))
                                         ]),
                                         not_followed_by = Fragment(IdentifierStart)
@@ -3686,8 +3689,11 @@ codegen_language_macros::compile!(Language(
                                     enabled = Till("0.5.0"),
                                     scanner = TrailingContext(
                                         scanner = Sequence([
-                                            Fragment(DecimalDigits),
-                                            Atom("."),
+                                            TrailingContext(
+                                                scanner =
+                                                    Sequence([Fragment(DecimalDigits), Atom(".")]),
+                                                not_followed_by = Fragment(DecimalDigits)
+                                            ),
                                             Optional(Fragment(DecimalExponent))
                                         ]),
                                         not_followed_by = Fragment(IdentifierStart)

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

@@ -820,9 +820,10 @@ slang_grammar! {
     scanner DecimalLiteral = (
         (
             (
-                { removed in "0.5.0"    (DecimalDigits (("." (DecimalDigits ?) ) ?)) } |
-                { introduced in "0.5.0" (DecimalDigits (("." DecimalDigits     ) ?)) } |
-                ('.' DecimalDigits)
+                (DecimalDigits not followed by '.') |
+                { removed in "0.5.0" ((DecimalDigits '.') not followed by DecimalDigits) } |
+                ('.' DecimalDigits) |
+                (DecimalDigits '.' DecimalDigits)
             )
             (DecimalExponent ?)
         ) not followed by IdentifierStart

crates/solidity/testing/snapshots/cst_output/NumericExpression/float_no_fraction/generated/0.5.0-failure.yml

@@ -5,15 +5,13 @@ Source: >
 
 Errors: # 1 total
   - >
-    Error: Expected DaysKeyword or EtherKeyword or FinneyKeyword or HoursKeyword or MinutesKeyword or SecondsKeyword or SzaboKeyword or WeeksKeyword or WeiKeyword.
-       ╭─[crates/solidity/testing/snapshots/cst_output/NumericExpression/float_no_fraction/input.sol:1:2]
+    Error: Expected DecimalLiteral or HexLiteral.
+       ╭─[crates/solidity/testing/snapshots/cst_output/NumericExpression/float_no_fraction/input.sol:1:1]
        │
      1 │ 1.
-       │  ┬  
+       │ ─┬  
        │  ╰── Error occurred here.
     ───╯
 
 Tree:
-  - NumericExpression (Rule): # 0..2 "1."
-      - DecimalLiteral (Token): "1" # 0..1
-      - SKIPPED (Token): "." # 1..2
+  - SKIPPED (Token): "1." # 0..2