RFR: 8284856: Add a test case for checking UnicodeScript entity numbers

[Naoto Sato]

Added the test case, and eliminated the immediate hashmap value, replaced with the ordinal number of `Character.UnicodeScript.UNKNOWN`.

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Depends on: https://git.openjdk.java.net/jdk/pull/7928

Commit messages:
 - 8284856: Add a test case for checking UnicodeScript entity numbers

Changes: https://git.openjdk.java.net/jdk/pull/8253/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8253&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8284856
  Stats: 13 lines in 2 files changed: 8 ins; 0 del; 5 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8253.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8253/head:pull/8253

PR: https://git.openjdk.java.net/jdk/pull/8253