Add XML documentation for Java.Time.Chrono

[jonathanpeppers]

The Java.Time.Chrono namespace contains 365 To be added placeholders in source XML documentation (excluding docs\xml\index.xml).

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

Update log

• 2026-09-10: Refreshed the placeholder scan from 380 to 365 (reduced by 15). Related documentation PRs: #467, #486, #644.