RFR: 8278349: JarSigner javadoc example uses SHA-1 [v2]

[Eirik Bjorsnos]

> Please review this trivial PR which updates javadoc sample code in jdk.security.jarsigner.JarSigner to use SHA-256, SHA256withRSA instead of the now considered weak algorithms SHA-1, SHA1withDSA.
> 
> The sample code is also updated to use the new snippet syntax.

Eirik Bjorsnos has updated the pull request incrementally with one additional commit since the last revision:

  Indent the javadoc code snippet to make it easier to separate from the snippet syntax

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Changes:
  - all: https://git.openjdk.org/jdk/pull/11992/files
  - new: https://git.openjdk.org/jdk/pull/11992/files/b288d1fd..56079e31

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=11992&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=11992&range=00-01

  Stats: 8 lines in 1 file changed: 0 ins; 0 del; 8 mod
  Patch: https://git.openjdk.org/jdk/pull/11992.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11992/head:pull/11992

PR: https://git.openjdk.org/jdk/pull/11992