RFR: JDK-8267219: Javadoc method summary breaks when {@inheritDoc} from an empty parent [v2]

[liach]

On Tue, 18 May 2021 13:52:25 GMT, Jonathan Gibbons <jjg at openjdk.org> wrote:

>> liach has refreshed the contents of this pull request, and previous commits have been removed. The incremental views will show differences compared to the previous content of the PR.
>
> As a matter of style, these days we avoid small files like `First.java` and `Second.java` and put the source instead in a text block in the main test file and write the file(s) on the fly, typically using `ToolBox.writeJavaFiles`.  This makes it easier to read the test all at once, instead of switching between small files that are dominated by a legal header.

Addressed both comments from @jonathan-gibbons and @hns.

Turns out the `isValid` check is way better, though it took me a bit of time to debug because the row supplied to the table was wrapped in a `ContentBuilder`, which did not have a proper implementation of `isValid` (so when it has an invalid but non-empty content, it reports itself as valid)

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PR: https://git.openjdk.java.net/jdk/pull/4066