json to g4 only with "parser" cause some syntax error

Grammar-Mutator `make` it, generate `Grammar.g4` is:
```
grammar Grammar;
entry
: node_A EOF
;
node_A
: node_NUMBER node_STRING '\n'
;
node_NUMBER
: '10'
| '99'
;
node_STRING
: '(' node_HEXSTRING ')'
;
node_HEXSTRING
:
| node_CHAR node_HEXSTRING
;
node_CHAR
: '0'
| '1'
| '2'
| '3'
| '4'
| '5'
| '6'
| '7'
| '8'
| '9'
| 'a'
| 'b'
| 'c'
| 'd'
| 'e'
| 'f'
;
```

we prepared input data `seed1 / seed2`, and use `antlr4-parse` to testing:


why is `10(10)` parsed incorrectly? because antlr4 is divided into two stages: lexer and parser. during lexer stage, `node_NUMBER:10` will be recognized as TOKEN, and in the parser stage, the result is `node_NUMBER (node_NUMBER)`, so an error occurred.

in the antlr4 grammar, lex rules begin with an uppercase letter, parser rules begin with a lowercase letter, so we should tell antlr4 the lexical rules clearly, patch `Grammar_patch.g4`:
```
grammar Grammar_patch;
entry
: node_A EOF
;
node_A
: node_NUMBER Node_STRING '\n'
;
node_NUMBER
: '10'
| '99'
;
Node_STRING
: '(' Node_HEXSTRING ')'
;
Node_HEXSTRING
:
| Node_CHAR Node_HEXSTRING
;
Node_CHAR
: '0'
| '1'
| '2'
| '3'
| '4'
| '5'
| '6'
| '7'
| '8'
| '9'
| 'a'
| 'b'
| 'c'
| 'd'
| 'e'
| 'f'
;
```

testing again:


>the "warning" prompts us it can match the empty string, this may cause antlr4 parsing backtrace issues, but we can easily mark it with `fragment Node_HEXSTRING`