RFR: 8283437: Refactor imageio classes javadoc to use @throws instead of @exception

[Prasanta Sadhukhan]

Prevailing JDK coding practices use "@throws" rather than "@exception".
Refactor existing imageio classes javadoc to use @throws

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Commit messages:
 - Fix
 - Fix
 - Fix

Changes: https://git.openjdk.java.net/jdk/pull/7885/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=7885&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8283437
  Stats: 775 lines in 51 files changed: 0 ins; 0 del; 775 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7885.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7885/head:pull/7885

PR: https://git.openjdk.java.net/jdk/pull/7885