Upgrade CI/CD to Saxon10 for XSLT support

[wendellpiez]

User Story:

An an open-source library Saxon9 should be useful for the indefinite future, however the current version Saxon10 is more performant and offer better (tighter) compile-time checks, for example.

Goals:

Let's upgrade Saxon9 to Saxon10 throughout the CI/CD pipelines. The invocation syntax is the same, so this mostly means integration and testing. Any newly discovered bugs in running code should be repaired etc.

As a follow-on task: references to Saxon9 throughout documentation (readmes) should be updated to say Saxon10.

(This was prompted by #1027.)

Dependencies:

None known.

Acceptance Criteria

• All OSCAL website and readme documentation affected by the changes in this issue have been updated. Changes to the OSCAL website can be made in the docs/content directory of your branch.
• A Pull Request (PR) is submitted that fully addresses the goals of this User Story. This issue is referenced in the PR.
• The CI-CD build process runs without any reported errors on the PR. This can be confirmed by reviewing that all checks have passed in the PR.

{The items above are general acceptance criteria for all User Stories. Please describe anything else that must be completed for this issue to be considered resolved.}