RFR: 8323158: HotSpot Style Guide should specify more include ordering

[Stefan Karlsson]

The HotSpot Style Guide has a section about source files and includes. The style used for includes have mostly been introduced by scripts when includeDB was replaced, but also when various other enhancements to our includes were made. Some of the introduced styles were never written down in the style guide.

I propose a couple of changes to the HotSpot Style Guide to reflect some of these implicit styles that we have. While updating the text I also took the liberty to order the items in an order that I felt was good.

Note that JDK-8323158 contains a few more suggestions, but I've only addressed the items that I think can be accepted without much contention. Either I extract the items that have not been address into a new RFE, or I create a new RFE for this PR.

There a some small whitespace tweaks that I made so that the .md and .html had a similar layout.

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Commit messages:
 - 8323158: HotSpot Style Guide should specify more include ordering

Changes: https://git.openjdk.org/jdk/pull/23388/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=23388&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8323158
  Stats: 46 lines in 2 files changed: 28 ins; 7 del; 11 mod
  Patch: https://git.openjdk.org/jdk/pull/23388.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/23388/head:pull/23388

PR: https://git.openjdk.org/jdk/pull/23388