RFR: 8241306: Add SignatureMethodParameterSpec subclass for RSASSA-PSS params [v6]

[Weijun Wang]

> This enhancement contains the following code changes:
> 
> 1. Create a new public API `javax/xml/crypto/dsig/spec/RSAPSSParameterSpec` and remove the internal one.
> 2. Update marshaling and unmarshaling code inside `DOMRSAPSSSignatureMethod` so it understands extra fields in `PSSParameterSpec` and is aware of the defaults in both directions.
> 3. Update `DOMSignedInfo` so that secure validation can restrict `DigestMethod` used inside `RSAPSSParameterSpec`
> 4. Tests

Weijun Wang has updated the pull request incrementally with one additional commit since the last revision:

  spec clarification

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/3181/files
  - new: https://git.openjdk.java.net/jdk/pull/3181/files/ce1678ea..a28a8fa1

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=3181&range=05
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=3181&range=04-05

  Stats: 67 lines in 5 files changed: 34 ins; 24 del; 9 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3181.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3181/head:pull/3181

PR: https://git.openjdk.java.net/jdk/pull/3181