Add a strongly typed AST

[felipebz]

Currently to create new rules it's necessary to know the internals of the grammar and look at the generated AST using the zpa-toolkit. Ideally we should provide an easier API to navigate through the AST.

Example:

zpa/plsql-custom-rules/src/main/java/com/company/plsql/ForbiddenDmlCheck.java

Lines 28 to 34 in 304aa89

	public void visitNode(AstNode node) {
	AstNode table = node.getFirstChild(DmlGrammar.TABLE_REFERENCE);
	if (table != null && table.getTokenOriginalValue().equalsIgnoreCase("user")) {
	addIssue(table, "Replace this query by a function of the USER_WRAPPER package.");
	}
	}

With a strongly typed AST it could be write like:

    public void visit(TableExpressionClause tableExpression) {
        TableReference table = tableExpression.getTableReference();
        
        if (table != null && table.getName().equalsIgnoreCase("user")) {
            addIssue(table, "Replace this query by a function of the USER_WRAPPER package.");
        }
    }

The SSLR library provides a API to create a typed AST but it only works with lexerless grammars, but we can't migrate to a lexerless grammar because it's much slower than the lexerful one.