Use disambiguated DecimalLiteral sub-rules in DSL v1

So that we minimize the parsing diff once migrate to DSL v2.

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