RFR: 8343239: Javadoc marks non-preview type as preview if it's the subtype of a preview type [v5]

[Nizar Benalla]

> Please review this patch to improve the javadoc preview header. The parent bug include more details.
> 
> This is meant to prevent a bug where, if a non preview class extend an `@PreviewFeature` interface, the Javadoc displays `Programs can only use <<Type>> when preview features are enabled` when the API can be used without enable preview features as long as we don't refer to any methods in the supertype
> 
> This is specifically the case in  #17543. Here is the javadoc output [AsymmetricKey](https://cr.openjdk.org/~nbenalla/GeneratedDocs/8343239-2/docs/api/java.base/java/security/AsymmetricKey.html) after merging this branch with the PR `298420: PEM API: Implementation (Preview) #17543`. The only files affected by this change are the class `DEREncodable` and it's Subinterfaces.
> 
> One other bug I noticed is that, on the `DEREncodable` page, it's direct subinterfaces had the superscript `PREVIEW` link. I've added a condition to remove it.

Nizar Benalla has updated the pull request incrementally with one additional commit since the last revision:

  Remove trailing whitespace attempt 2

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/22126/files
  - new: https://git.openjdk.org/jdk/pull/22126/files/f3582d65..06f5c750

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=22126&range=04
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=22126&range=03-04

  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/22126.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/22126/head:pull/22126

PR: https://git.openjdk.org/jdk/pull/22126