RFR: 8245095: Implementation of JEP 408: Simple Web Server [v2]

[Julia Boes]

> This change implements a simple web server that can be run on the command-line with `java -m jdk.httpserver`.
> 
> This is facilitated by adding an entry point for the `jdk.httpserver` module, an implementation class whose main method is run when the above command is executed. This is the first such module entry point in the JDK.
> 
> The server is a minimal HTTP server that serves the static files of a given directory, similar to existing alternatives on other platforms and convenient for testing, development, and debugging.
> 
> Additionally, a small API is introduced for programmatic creation and customization.
> 
> Testing: tier1-3.

Julia Boes has updated the pull request incrementally with three additional commits since the last revision:

 - small spec rewording
 - add module main class to symbolgenerator
 - remove UnmodifiableHeaders constant

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/5505/files
  - new: https://git.openjdk.java.net/jdk/pull/5505/files/093263d0..f53c59d9

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=5505&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=5505&range=00-01

  Stats: 32 lines in 3 files changed: 25 ins; 2 del; 5 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5505.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5505/head:pull/5505

PR: https://git.openjdk.java.net/jdk/pull/5505