RFR: 8273355: Flickering on tooltip appearance IntelliJ IDEA 2021.2.1 [v3]

[Alexey Ushakov]

> Used setOpaque() method to set correct background of platform window
> Extracted setting background to the particular method in PlatformWindow. Provided appropriate implementation in CPlatformWindow.

Alexey Ushakov has updated the pull request incrementally with one additional commit since the last revision:

  8273355: Flickering on tooltip appearance IntelliJ IDEA 2021.2.1
  
  Copyright update

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/7931/files
  - new: https://git.openjdk.java.net/jdk/pull/7931/files/8faccd68..9ecf1b30

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=7931&range=02
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=7931&range=01-02

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7931.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7931/head:pull/7931

PR: https://git.openjdk.java.net/jdk/pull/7931