RFR: 8242077: Add information about HTTP/2 and HttpClient usage in WebEngine

[Abhinay Agarwal]

Update WebEngine's Javadoc to add information on how it switches to HttpClient instead of URLConnection in JavaFX 14
when used with JDK 12 or later.

Identification the correct client is important as both these clients may offer different ways to achieve a task. One
such task can be bypassing insecure HTTPS connection.

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Commit messages:
 - Remove trailing whitespace
 - 8242077: Add information about HTTP/2 and HttpClient usage in WebEngine

Changes: https://git.openjdk.java.net/jfx/pull/189/files
 Webrev: https://webrevs.openjdk.java.net/jfx/189/webrev.00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8242077
  Stats: 6 lines in 1 file changed: 6 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jfx/pull/189.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/189/head:pull/189

PR: https://git.openjdk.java.net/jfx/pull/189