RFR: 8369531: Wrong generic tooltip used in external class links [v2]

[Hannes Wallnöfer]

> Please review a change to use the same title attribute (tooltip) in external class links as in internal ones. 
> 
> Currently, links to external types and their members always use `class or interface in x.y.z` as tooltip. This is unecessarily generic for type links, because we actually know whether it is a class or an interface, and already have the correct tooltip message. For member links, it is misleading because the link target is not the class or interface.
> 
> With this change, external links use the same tooltip as internal ones. Links to top-level types specify whether it is a class or interface. Links to methods use the method signature as tooltip if the link label only contains the method name. For other members, the no tooltip is set. 
> 
> I'm also removing the `doclet.Href_Class_Or_Interface_Title` message because it is not used anymore.

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

  Add @bug id

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Changes:
  - all: https://git.openjdk.org/jdk/pull/28491/files
  - new: https://git.openjdk.org/jdk/pull/28491/files/8e4138c5..dbf2c4d7

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=28491&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=28491&range=00-01

  Stats: 5 lines in 5 files changed: 1 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/28491.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/28491/head:pull/28491

PR: https://git.openjdk.org/jdk/pull/28491