RFR: JDK-8274639: Provide a way to disable warnings for cross-modular links [v4]

[Hannes Wallnöfer]

> This is a simple change to add a new `--link-modularity-mismatch (warn|info)` command line option to allow messages about wrong modularity of externally linked documentation bundles to be issued as warnings or notices. 
> 
> CSR: https://bugs.openjdk.java.net/browse/JDK-8274969

Hannes Wallnöfer has updated the pull request incrementally with one additional commit since the last revision:

  More review feedback

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/5900/files
  - new: https://git.openjdk.java.net/jdk/pull/5900/files/db81fc42..cddace7f

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=5900&range=03
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=5900&range=02-03

  Stats: 10 lines in 3 files changed: 2 ins; 0 del; 8 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5900.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5900/head:pull/5900

PR: https://git.openjdk.java.net/jdk/pull/5900