Move test for dates before start of the Japanese era into a new file

See also <https://github.com/tc39/proposal-temporal/issues/2865>
requesting for more information how this case should actually be
handled.

test/staging/Intl402/Temporal/old/japanese-before-era.js

@@ -0,0 +1,63 @@
+// Copyright (C) 2018 Bloomberg LP. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal-intl
+description: Japanese eras
+features: [Temporal]
+---*/
+
+// Dates in same year before Japanese era starts will resolve to previous era
+var date = Temporal.PlainDate.from({
+  era: "reiwa",
+  eraYear: 1,
+  month: 1,
+  day: 1,
+  calendar: "japanese"
+});
+assert.sameValue(`${ date }`, "2019-01-01[u-ca=japanese]");
+assert.sameValue(date.era, "heisei");
+assert.sameValue(date.eraYear, 31);
+
+date = Temporal.PlainDate.from({
+  era: "heisei",
+  eraYear: 1,
+  month: 1,
+  day: 1,
+  calendar: "japanese"
+});
+assert.sameValue(`${ date }`, "1989-01-01[u-ca=japanese]");
+assert.sameValue(date.era, "showa");
+assert.sameValue(date.eraYear, 64);
+date = Temporal.PlainDate.from({
+  era: "showa",
+  eraYear: 1,
+  month: 1,
+  day: 1,
+  calendar: "japanese"
+});
+assert.sameValue(`${ date }`, "1926-01-01[u-ca=japanese]");
+assert.sameValue(date.era, "taisho");
+assert.sameValue(date.eraYear, 15);
+
+date = Temporal.PlainDate.from({
+  era: "taisho",
+  eraYear: 1,
+  month: 1,
+  day: 1,
+  calendar: "japanese"
+});
+assert.sameValue(`${ date }`, "1912-01-01[u-ca=japanese]");
+assert.sameValue(date.era, "meiji");
+assert.sameValue(date.eraYear, 45);
+
+date = Temporal.PlainDate.from({
+  era: "meiji",
+  eraYear: 1,
+  month: 1,
+  day: 1,
+  calendar: "japanese"
+});
+assert.sameValue(`${ date }`, "1868-01-01[u-ca=japanese]");
+assert.sameValue(date.era, "ce");
+assert.sameValue(date.eraYear, 1868);

test/staging/Intl402/Temporal/old/japanese-era.js

@@ -58,61 +58,6 @@ var date = Temporal.PlainDate.from({
 });
 assert.sameValue(`${ date }`, "1869-01-01[u-ca=japanese]");
 
-// Dates in same year before Japanese era starts will resolve to previous era
-var date = Temporal.PlainDate.from({
-  era: "reiwa",
-  eraYear: 1,
-  month: 1,
-  day: 1,
-  calendar: "japanese"
-});
-assert.sameValue(`${ date }`, "2019-01-01[u-ca=japanese]");
-assert.sameValue(date.era, "heisei");
-assert.sameValue(date.eraYear, 31);
-
-date = Temporal.PlainDate.from({
-  era: "heisei",
-  eraYear: 1,
-  month: 1,
-  day: 1,
-  calendar: "japanese"
-});
-assert.sameValue(`${ date }`, "1989-01-01[u-ca=japanese]");
-assert.sameValue(date.era, "showa");
-assert.sameValue(date.eraYear, 64);
-date = Temporal.PlainDate.from({
-  era: "showa",
-  eraYear: 1,
-  month: 1,
-  day: 1,
-  calendar: "japanese"
-});
-assert.sameValue(`${ date }`, "1926-01-01[u-ca=japanese]");
-assert.sameValue(date.era, "taisho");
-assert.sameValue(date.eraYear, 15);
-
-date = Temporal.PlainDate.from({
-  era: "taisho",
-  eraYear: 1,
-  month: 1,
-  day: 1,
-  calendar: "japanese"
-});
-assert.sameValue(`${ date }`, "1912-01-01[u-ca=japanese]");
-assert.sameValue(date.era, "meiji");
-assert.sameValue(date.eraYear, 45);
-
-date = Temporal.PlainDate.from({
-  era: "meiji",
-  eraYear: 1,
-  month: 1,
-  day: 1,
-  calendar: "japanese"
-});
-assert.sameValue(`${ date }`, "1868-01-01[u-ca=japanese]");
-assert.sameValue(date.era, "ce");
-assert.sameValue(date.eraYear, 1868);
-
 // Verify that CE and BCE eras (before Meiji) are recognized
 date = Temporal.PlainDate.from({
   era: "ce",