RFR: 8368695: Support 101 switching protocol in jdk.httpserver [v13]

[Josiah Noel]

> - adds a flag to ExchangeImpl to signal whether the current request is an Upgrade request
> - Adds a new `UpgradeInputStream` to ensure that the server keeps track of when the upgraded request is closed
> - on 101 response codes, `sendResponseHeaders` will not immediately close the output stream 
> - on 101 response codes, `sendResponseHeaders` will use an `UndefLengthOutputStream`

Josiah Noel has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 18 commits:

 - Update ExchangeImpl.java
 - Merge remote-tracking branch 'upstream/master' into JDK-8368695
 - reduce diff
 - Merge remote-tracking branch 'upstream/master' into JDK-8368695
 - Update SwitchingProtocolTest.java
 - Update SwitchingProtocolTest.java
 - Update SwitchingProtocolTest.java
 - add exception test
 - Create UpgradeOutputStream.java
 - close raw streams
 - ... and 8 more: https://git.openjdk.org/jdk/compare/32697bf6...ae2b1184

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Changes: https://git.openjdk.org/jdk/pull/27751/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=27751&range=12
  Stats: 25304 lines in 632 files changed: 6529 ins; 14641 del; 4134 mod
  Patch: https://git.openjdk.org/jdk/pull/27751.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27751/head:pull/27751

PR: https://git.openjdk.org/jdk/pull/27751