RFR: 8276124: Provide snippet support for properties files [v2]

[Pavel Rappo]

> The initial integration (JDK-8266666) of JEP 413 did not support properties files. This commit rights that wrong.

Pavel Rappo has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase.

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/6397/files
  - new: https://git.openjdk.java.net/jdk/pull/6397/files/2e43402e..2e43402e

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=6397&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=6397&range=00-01

  Stats: 0 lines in 0 files changed: 0 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6397.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6397/head:pull/6397

PR: https://git.openjdk.java.net/jdk/pull/6397