Add XML documentation for Java.Util.Jar

[jonathanpeppers]

The Java.Util.Jar namespace contains 387 To be added placeholders in source XML documentation (excluding docs\xml\index.xml).

rg -n -i --glob 'Java.Util.Jar/**' --glob 'ns-Java.Util.Jar.xml' 'to be added' docs\xml

Update log

• 2026-09-10: Refreshed the placeholder scan from 407 to 387 (reduced by 20). Related documentation PRs: #468, #473, #504, #507, #618, #644.