RFR: 8352249: Remove incidental whitespace in traditional doc comments [v2]

[Hannes Wallnöfer]

> Please review a patch to remove incidental indentation from traditional doc comments. This adds a `stripIndent()` method to the `Tokens.Comment` interface and a new `JavadocTokenizer.StrippedComment` nested class that implements indentation stripping while maintaining a map of position offsets to the original comment. 
> 
> While the patch changes `javadoc` output by removing leading whitespace, the change is generally not visible in the browser except in `<pre>` elements, which is the point of this enhancement. 
> 
> The change affects most tree positions in the AST checker tests in javac/doctree, but mostly does not affect the structure of the parsed trees, with the exception of `BreakIterator` tests in `FirstSentenceTest.java`. 
> 
> `BreakIterator` does not recognize `.\n` immediately followed by a lower case letter as sentence break, while it recognizes the break if the letter is an upper-case letter *or* if there is a space between the line break and the letter. I find this rule a bit peculiar but AFAICT we can't influence the behavior of `BreakIterator`, so I have added tests that cover both lower and upper-case behavior.
> 
> The source position lookup in the stripped comment is implemented by creating a new `OffsetMap` that translates from the stripped to the original comment, then using the original comment's `OffsetMap` to translate the position to the source file. `OffsetMap` is relatively lightweight (usually 2 `int[]` elements per comment paragraph), so the added overhead is not too bad. 
> 
> Inspired by [JDK-8305688](https://bugs.openjdk.org/browse/JDK-8305688) I did various test builds with restricted jobs and memory settings, but didn't notice any change in processing or memory overhead to API docs builds.

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

  Whitespace normalization in PrettyCheck becomes simpler

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/24032/files
  - new: https://git.openjdk.org/jdk/pull/24032/files/eb9a090c..1c21de77

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=24032&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=24032&range=00-01

  Stats: 55 lines in 3 files changed: 0 ins; 48 del; 7 mod
  Patch: https://git.openjdk.org/jdk/pull/24032.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/24032/head:pull/24032

PR: https://git.openjdk.org/jdk/pull/24032