RFR: JDK-8266503: [UL] Make Decorations safely copy-able and reduce their size [v4]

[Thomas Stuefe]

> This patch reduces the size of UL `LogDecorations` by about 85% (from 368 -> 56 bytes on Linux x64). This matters in the context of asynchronous logging in UL where we plan to keep a buffer containing log messages, including decorations, for asynchronous printing.
> 
> As a side effect, it makes the LogDecorations object safe to copy with trivial assignment constructors and operators (which it had not been before).
> 
> As another side effect, the 256-char-for-all-decorators limit has been removed with this patch.
> 
> What the patch does:
> 
> In LogDecorations, we resolve the values of the given decorators ("uptime", "tid" etc) and print them in human-readable format. Before this patch, the class LogDecorations stored the printed decorators in an internal (limited, fixed-sized) buffer. This is inefficient since this takes much more memory than storing the binary data before printing them.
> 
> So this patch separates the decorator value resolving from the printing. It stores the resolved values in binary form and only prints them when needed. Since a decorations object is only printed once this is fine. No need to cache the formatted text.
> 
> *Please Note that this patch includes the fix for JDK-8266536: "Provide a variant of os::iso8601_time which works with arbitrary timestamps" which is in a separate PR (https://github.com/openjdk/jdk/pull/3869) - so please ignore all the iso6801 stuff. It also contains a fix for the broken harfbuzz build.*
> 
> Testing:
> - gtests, manually
> - jtreg runtime/logging, manually
> - SAP nightlies ran fine, but since then the tests changed, will run them again tonight

Thomas Stuefe has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains ten commits:

 - Merge
 - Xins debug check proposal
 - LogTagSet::describe_tagsets can use the stream interface of label and avoid copying
 - Merge
 - Remove harfbuzz build fix
 - Volker feedback
 - start
 - cherry-picked JDK-8266536
 - harfbuzz-buildfix

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

Changes: https://git.openjdk.java.net/jdk/pull/3874/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=3874&range=03
  Stats: 169 lines in 7 files changed: 64 ins; 34 del; 71 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3874.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3874/head:pull/3874

PR: https://git.openjdk.java.net/jdk/pull/3874