RFR: 8274255: Update javac messages to use "enum class" rather than "enum type"

[Joe Darcy]

As a belated part of the terminology update (JDK-8246772), change

enum type -> enum class
annotation type -> annotation interface

in javac's compiler.properties files. General analysis of the use of "type" in that file is beyond the scope of this PR.

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Commit messages:
 - 8274255: Update javac messages to use "enum class" rather than "enum type"

Changes: https://git.openjdk.java.net/jdk/pull/5689/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=5689&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8274255
  Stats: 22 lines in 1 file changed: 0 ins; 0 del; 22 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5689.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5689/head:pull/5689

PR: https://git.openjdk.java.net/jdk/pull/5689