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

[Ian Graves]

On Fri, 26 Mar 2021 00:28:15 GMT, Tagir F. Valeev <tvaleev at openjdk.org> wrote:

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

This is related to a conversation we had on a [different PR](https://github.com/openjdk/jdk/pull/2979#issuecomment-817075524) where this fix was slightly out of band for the rest of the bug. Changes look good to me, though I am not yet a reviewer. Thanks for pulling this together here @amaembo !

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