RFR: JDK-8254721: Improve support for conditionally generated files [v2]

[Jonathan Gibbons]

> The overall pages is very dynamic and depends on a lot of factors, such as the input files and the command-line
> options. Some of the summary files depend on the content of the classes being documented, such as:
> * any constant values declared in the files
> * any deprecated elements
> * any serializable classes
> * any classes whose description references system properties
> 
> This change is a step towards handling these files in a uniform manner.
> 
> There is a new test to test the consistency of the new behavior..

Jonathan Gibbons has updated the pull request incrementally with one additional commit since the last revision:

  Address minor review feedback

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/674/files
  - new: https://git.openjdk.java.net/jdk/pull/674/files/dbb04225..3efdd958

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=674&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=674&range=00-01

  Stats: 20 lines in 8 files changed: 0 ins; 1 del; 19 mod
  Patch: https://git.openjdk.java.net/jdk/pull/674.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/674/head:pull/674

PR: https://git.openjdk.java.net/jdk/pull/674