RFR: JDK-8264221: Rewrite confusing stream API chain in SnippetMaps

[Tagir F.Valeev]

I also simplified a couple of other places: replaced `stream().forEach()` with just `forEach()` and removed redundant `length()` argument in `substring()` call.

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Commit messages:
 - SnippetMaps updated

Changes: https://git.openjdk.java.net/jdk/pull/3209/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=3209&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8264221
  Stats: 12 lines in 1 file changed: 3 ins; 3 del; 6 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3209.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3209/head:pull/3209

PR: https://git.openjdk.java.net/jdk/pull/3209