RFR: 8266666: Implementation for snippets [v17]

[Pavel Rappo]

> This PR implements JEP 413 "Code Snippets in Java API Documentation", which hasn't been yet proposed to target JDK 18. The PR starts as a squashed merge of the https://github.com/openjdk/jdk-sandbox/tree/jdk.javadoc/snippets branch.

Pavel Rappo has refreshed the contents of this pull request, and previous commits have been removed. The incremental views will show differences compared to the previous content of the PR. The pull request contains one new commit since the last revision:

  Format code closer to the ambient style
  
  Makes new constructs look more natural in their context by adopting the surrounding style.

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/4795/files
  - new: https://git.openjdk.java.net/jdk/pull/4795/files/6c33cb6a..9ab2cbdd

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=4795&range=16
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=4795&range=15-16

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4795.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4795/head:pull/4795

PR: https://git.openjdk.java.net/jdk/pull/4795