RFR: 8267329: Modernize Javadoc code to use instanceof with pattern matching [v3]

[Jonathan Gibbons]

On Wed, 19 May 2021 22:06:18 GMT, Jonathan Gibbons <jjg at openjdk.org> wrote:

>> Unclear if there's a more succinct way to refactor this like so. If `c` is not an instance of `TextBuilder` then we need to initialize a new `TextBuilder` and add it to `contents`. This is not the case if `c` is already of the desired instance.
>
> Then just a shorter name than `txtBldr` please. Lvng t vwls s nt - jvdc cnvntn.

I guess we have competing demands for short names!

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PR: https://git.openjdk.java.net/jdk/pull/4105