RFR: JDK-8264274: Block tags in overview.html are ignored [v2]

[Hannes Wallnöfer]

> This is a simple fix to generate block tags in overview files specified by the `-overview` option. 
> 
> I added a protected `addOverviewTags` method in `AbstractOverviewIndexWriter` which is probably overkill but keeps things flexible and separated.

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

  JDK-8264274: Simplify format specifier

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/5099/files
  - new: https://git.openjdk.java.net/jdk/pull/5099/files/bcec66cb..8b781ea2

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=5099&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=5099&range=00-01

  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5099.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5099/head:pull/5099

PR: https://git.openjdk.java.net/jdk/pull/5099