SimpleXmlParser: Processing instructions are not handled

[ljnelson]

Permitted states do not include processing instructions:

https://github.com/oracle/helidon-build-tools/blob/d216b571bb03abd5b08f5a6c65077892e373a871/common/xml/src/main/java/io/helidon/build/common/xml/SimpleXMLParser.java#L226-L239

The manifesting symptom is that in a processing instruction like this:

<?m2e execute onConfiguration,onIncremental?>

…the parser bails out here:

https://github.com/oracle/helidon-build-tools/blob/d216b571bb03abd5b08f5a6c65077892e373a871/common/xml/src/main/java/io/helidon/build/common/xml/SimpleXMLParser.java#L593-L594

[romain-grecourt]

Steps to reproduce with the helidon cli:

• generate a quickstart/mp project
• edit jandex-maven-plugin execution like this:

<plugin>
    <groupId>org.jboss.jandex</groupId>
    <artifactId>jandex-maven-plugin</artifactId>
    <executions>
        <execution>
            <?m2e execute onConfiguration,onIncremental?>
            <id>make-index</id>
        </execution>
    </executions>
</plugin>

• remove .helidon
• run helidon dev