RFR: 8286872: Refactor add/modify notification icon (TrayIcon)

[Alexey Ivanov]

Encapsulate the logic of adding or modifying a notification icon aka tray icon. This is to avoid code duplication between [`AwtTrayIcon::WmTaskbarCreated`](https://github.com/openjdk/jdk/blob/7b988b31c661c6e3e58cf8ced81732e40a79d4f5/src/java.desktop/windows/native/libawt/windows/awt_TrayIcon.cpp#L477) and [`AwtTrayIcon::_UpdateIcon`](https://github.com/openjdk/jdk/blob/7b988b31c661c6e3e58cf8ced81732e40a79d4f5/src/java.desktop/windows/native/libawt/windows/awt_TrayIcon.cpp#L796).

Separating adding and modifying the icon simplifies the methods, the actions are clearer: adding the icon requires sending `NIM_SETVERSION` message whereas modifying the icon doesn't.

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Depends on: https://git.openjdk.java.net/jdk/pull/8441

Commit messages:
 - 8286872: Refactor add/modify notification icon (TrayIcon)

Changes: https://git.openjdk.java.net/jdk/pull/8749/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8749&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8286872
  Stats: 26 lines in 2 files changed: 17 ins; 4 del; 5 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8749.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8749/head:pull/8749

PR: https://git.openjdk.java.net/jdk/pull/8749