Consistent naming for combined and separated grammars

Here is the current naming:
### Combined

```
grammar Foo;
```
- `FooLexer`, `FooParser`
- `FooListener`, `FooBaseListener`
- `FooParseListener`, `FooBaseParseListener`
- `FooVisitor`, `FooBaseVisitor`
### Separated

```
lexer grammar FooLexer;
parser grammar FooParser;
```
- `FooLexer`, `FooParser`
- `FooParserListener`, `FooParserBaseListener`
- `FooParserParseListener`, `FooParserBaseParseListener`
- `FooParserVisitor`, `FooParserBaseVisitor`
### Request

I find that in ANTLR 4 I'm more likely to use separated grammars than combined grammars. However, I wish the names of listeners/visitors generated by the separated grammars to match those of the combined grammar. In particular, if (and only if) a parser grammar is named `*Parser`, I'd like to drop the `Parser` suffix as part of deriving the generated file names.

No files or tests are named in the issue. Start by locating how grammar names derive generated listener and visitor filenames; done means a separated parser grammar named with a Parser suffix produces the same listener and visitor names as the equivalent combined grammar, without changing other naming cases.

Written by the indexing model from the issue text.