Add gradle task 'aggregateJavadocIncludingTests' that builds javadoc for both main and test
Add gradle task 'aggregateJavadocIncludingTests' that builds javadoc for both main and test

It will allow CI to spot javadoc errors, for example broken links, in test code.

Close apache/calcite-avatica#117

looker-open-source/calcite-avatica,looker-open-source/calcite-avatica,looker-open-source/calcite-avatica,apache/calcite-avatica,looker-open-source/calcite-avatica,apache/calcite-avatica,apache/calcite-avatica,apache/calcite-avatica,looker-open-source/calcite-avatica,apache/calcite-avatica