RFR: 8270286: com.sun.net.httpserver.spi.HttpServerProvider: remove use of deprecated API

[Julia Boes]

This is a cleanup fix that replaces the deprecated method `Class::newInstance()` with `cls.getDeclaredConstructor().newInstance()` when loading the provider.

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Commit messages:
 - initial commit

Changes: https://git.openjdk.java.net/jdk/pull/4789/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=4789&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8270286
  Stats: 153 lines in 2 files changed: 147 ins; 0 del; 6 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4789.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4789/head:pull/4789

PR: https://git.openjdk.java.net/jdk/pull/4789