Fix Temporal calendar handling and enable 2,782 more test262 passes

[lahma]

Summary

• Fix with() for Gregorian-based calendars (buddhist/roc/japanese) in PlainDateTime, ZonedDateTime, PlainYearMonth — route through CalendarDateToISO instead of treating calendar year as ISO year
• Fix dayOfYear for non-ISO calendars — return calendar-aware day-of-year instead of ISO day-of-year
• Reject islamic/islamic-rgsa calendars in Temporal from() constructors (observation-based, not supported for arithmetic)
• Add missing era/eraYear field reading in ZonedDateTime.prototype.with()
• Fix month/monthCode priority in non-ISO with() — when monthCode is explicitly provided but month is not, avoid conflict with defaulted month value
• Fix single-era calendars (coptic, hebrew, persian, indian, ethioaa) to always return primary era regardless of year sign
• Accept ad/bc as era code aliases for ce/bce in Japanese calendar
• Fix Japanese Meiji era offset (eraYear + 1867), display boundary (year >= 1873), and year-level boundary (no day-level check for Meiji)
• Fix invalid monthCode rejection (M14 for 13-month calendars, M13 for 12-month calendars)
• Consolidate duplicated monthCode validation into ValidateMonthCodeForNonLeapCalendar helper

Before: 93,206 test262 passes, ~343 excluded intl402/Temporal files
After: 95,988 test262 passes, 215 excluded intl402/Temporal files (+2,782 passes, 128 fewer exclusions)

Test plan

• dotnet test --configuration Release Jint.Tests.Test262/Jint.Tests.Test262.csproj — 95,988 passed, 0 failed
• dotnet test --configuration Release Jint.Tests/Jint.Tests.csproj — 2,764 passed, 0 failed
• No regressions in existing tests

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