RFR: 8285611: Retrofit (Doc)Pretty with java.io.UncheckedIOException

[Pavel Rappo]

Standard `java.io.UncheckedIOException` is more convenient than older ad-hoc `com.sun.tools.javac.tree.(Doc)Pretty.UncheckedIOException`.

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Commit messages:
 - Initial commit

Changes: https://git.openjdk.java.net/jdk/pull/8387/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8387&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8285611
  Stats: 20 lines in 2 files changed: 1 ins; 16 del; 3 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8387.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8387/head:pull/8387

PR: https://git.openjdk.java.net/jdk/pull/8387