RFR: 8293630: Simplify TreeMap.get() with Comparator.naturalOrder() [v2]

[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 P.S. I think the comment of `TreeMap.getEntryUsingComparator()` is outdated.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:

  Update src/java.base/share/classes/java/util/TreeMap.java
  
  Co-authored-by: ExE Boss <3889017+ExE-Boss at users.noreply.github.com>

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Changes:
  - all: https://git.openjdk.org/jdk/pull/9901/files
  - new: https://git.openjdk.org/jdk/pull/9901/files/259348a7..ab4cfa2c

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=9901&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=9901&range=00-01

  Stats: 5 lines in 1 file changed: 4 ins; 0 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