RFR: JDK-8282696: Add constructors taking a cause to InvalidObjectException and InvalidClassException [v6]

[Joe Darcy]

> Occasionally in core-libs we've discussed whether or not to do a pass over the exception classes and proactively add any of four missing convention constructors per java.lang.Throwable (no-arg, string, cause, cause and string). Last time this came up, we decided a wide-scale effort wasn't worthwhile.
> 
> Prompted by some other recent work, I decided to take a quick look at the dual-approach: grep for calls to initCause in java.base and seeing which exception classes repeated were initCaused. Those exception classes are good candidates for cause-taking constructors.
> 
> Two such exception classes area InvalidObjectException and InvalidClassException, along with their superclass ObjectStreamException.
> 
> Please also review the CSR: https://bugs.openjdk.java.net/browse/JDK-8282697

Joe Darcy has updated the pull request incrementally with one additional commit since the last revision:

  Reflow per review comments.

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/7711/files
  - new: https://git.openjdk.java.net/jdk/pull/7711/files/2de370f7..2aeb7f03

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=7711&range=05
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=7711&range=04-05

  Stats: 2 lines in 1 file changed: 0 ins; 1 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7711.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7711/head:pull/7711

PR: https://git.openjdk.java.net/jdk/pull/7711