RFR: 8293630: Simplify TreeMap.get() with Comparator.naturalOrder() [v4]

[Сергей Цыпанов]

> We can use `Comparator.naturalOrder()` for cases when a `TreeMap` instance is constructed without comparator. This allows to squash two branches in `TreeMap.get()` into one.
> 
> P.S. I think the comment of `TreeMap.getEntryUsingComparator()` is outdated. Should we also change it?

Сергей Цыпанов has updated the pull request incrementally with one additional commit since the last revision:

  8293630: Inline natural()

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Changes:
  - all: https://git.openjdk.org/jdk/pull/9901/files
  - new: https://git.openjdk.org/jdk/pull/9901/files/a55957e9..ae6e2320

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=9901&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=9901&range=02-03

  Stats: 8 lines in 1 file changed: 2 ins; 5 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/9901.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9901/head:pull/9901

PR: https://git.openjdk.org/jdk/pull/9901