RFR: 8308016: Use snippets in java.io package [v6]

[Brian Burkhalter]

> Replace `<pre>{@code ...}</pre>` patterns and the like with `{@snippet lang=java : ...}`.

Brian Burkhalter has updated the pull request incrementally with one additional commit since the last revision:

  8308016: Reinstate @snippet for RandomAccessFile::readLong

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Changes:
  - all: https://git.openjdk.org/jdk/pull/13957/files
  - new: https://git.openjdk.org/jdk/pull/13957/files/724a74a9..8ae42cf2

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=13957&range=05
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=13957&range=04-05

  Stats: 3 lines in 1 file changed: 0 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/13957.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13957/head:pull/13957

PR: https://git.openjdk.org/jdk/pull/13957