RFR: 8374808: Add new methods to KeyStore and KeyStoreSpi that return the creation date as an Instant instead of Date [v3]

[Mikhail Yankelevich]

> Hi!
> 
> This is my proposal to transfer `KeyStore` and `KeyStoreSpi` with internal implementations to use `Instance`s instead of `Date`s. 
> I would be very grateful for your comments and suggestions.
> 
> Thanks!
> 
> P.S. this is related to [JDK-8350953](https://bugs.openjdk.org/browse/JDK-8350953)

Mikhail Yankelevich has updated the pull request incrementally with one additional commit since the last revision:

  documentation change and truncated instances to millis

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/29140/files
  - new: https://git.openjdk.org/jdk/pull/29140/files/6c35e980..a7fd4678

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=29140&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=29140&range=01-02

  Stats: 44 lines in 7 files changed: 4 ins; 19 del; 21 mod
  Patch: https://git.openjdk.org/jdk/pull/29140.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/29140/head:pull/29140

PR: https://git.openjdk.org/jdk/pull/29140