Refactor package to allow clients to use Java Modules

When trying to use both `gremlin-core` and `gremlin-language` in a java modules build it fails with,

module org.sqlg reads package org.apache.tinkerpop.gremlin.language.grammar from both gremlin.language and gremlin.core

When building using java modules the following code is needed in module-info.java

module org.sqlg {
    requires gremlin.core;
    requires gremlin.language;
    requires gremlin.shaded;
}

Both gremlin-core and gremlin-language have the package

org.apache.tinkerpop.gremlin.language.grammar

This is called a split package and it not allowed by the java module system.

Seeing as Gremlin.g4 generates into org.apache.tinkerpop.gremlin.language.grammar I suggest renaming org.apache.tinkerpop.gremlin.language.grammar to something else in gremlin-core.

On my local machine I renamed gremlin-core/org.apache.tinkerpop.gremlin.language.grammar to org.apache.tinkerpop.gremlin.language.grammar2 which resolved the issue.