RFR: 8301260: Add system property to toggle XML Signature secure validation mode [v3]

[Sean Mullan]

> This change adds a system property that can be used to enable/disable the XML Signature secure validation mode. This is useful for enabling/disabling the mode at runtime. The system property will supersede and have the same name as the XMLCryptoContext property that can be used to enable/disable the mode: "org.jcp.xml.dsig.secureValidation".

Sean Mullan has updated the pull request incrementally with one additional commit since the last revision:

  Remove trailing whitespace.

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Changes:
  - all: https://git.openjdk.org/jdk/pull/12365/files
  - new: https://git.openjdk.org/jdk/pull/12365/files/bc77ee05..949f671a

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=12365&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=12365&range=01-02

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/12365.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12365/head:pull/12365

PR: https://git.openjdk.org/jdk/pull/12365