RFR: 8369995: Implement extra logging and/or propagate errors in X509KeyManagerImpl and fix StringIndexOutOfBoundsException [v6]

[Mikhail Yankelevich]

> In [JDK-8309667](https://bugs.openjdk.org/browse/JDK-8309667), there were issues with debugging due to no logging or throwing of errors by X509KeyManagerImpl::getEntry. [Line](https://github.com/openjdk/jdk/blob/6a4c2676a6378f573bd58d1bc32b57765d756291/src/java.base/share/classes/sun/security/ssl/X509KeyManagerImpl.java#L243-L245)
> 
> Extra logging and error propagating should be implemented for the X509KeyManagerImpl.
> 
> Additionally, dot checking logic has been changed, so no cases similar to `.A` will not trigger StringOutOfBounds exceptions. 
> 
> Thank you @djelinski for finding the issue and analysis.

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

  Artur's comments

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Changes:
  - all: https://git.openjdk.org/jdk/pull/27851/files
  - new: https://git.openjdk.org/jdk/pull/27851/files/a44f2b8f..370a1538

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=27851&range=05
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=27851&range=04-05

  Stats: 7 lines in 1 file changed: 1 ins; 1 del; 5 mod
  Patch: https://git.openjdk.org/jdk/pull/27851.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27851/head:pull/27851

PR: https://git.openjdk.org/jdk/pull/27851