RFR: 8286180: Enable construction of LogStreamImpl from LogMessageImpl [v6]

[Johan Sjölén]

> May I please have a review of this PR which adds non-interleaving log streams to UL?
> 
> In `LogMessageImpl` I remove templates and instead directly store a reference to `LogTagSet` and change `LogTagHandle` to be consistent (from pointer to reference) with `LogMessageImpl`.
> 
> Adding a non-interleaving log stream enables UL to replace two patterns found in HotSpot:
> 
> 1. `ttyLocker` + `(x)tty`
> Instead of taking the global tty lock in order to ensure non-interleaving logs we can now make a `NonInterleavingLogstream` and pass that around to various `print_on(outputStream*)` functions.
> 
> 2. `stringStream` + `outputStream*`
> In order to avoid taking the lock and being able to take arbitrary output streams a `stringStream` is created and finally printed through `print_raw(ss.as_string())`. This however requires a `ResourceMark`, which `NonInterleavingLogStream` does not require.
> 
> Passes tier 1.

Johan Sjölén has updated the pull request incrementally with three additional commits since the last revision:

 - Minor style fixes
 - Call renamed function
 - Fix indentation nit

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/8748/files
  - new: https://git.openjdk.java.net/jdk/pull/8748/files/c04e06be..a8832d74

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=8748&range=05
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=8748&range=04-05

  Stats: 10 lines in 3 files changed: 2 ins; 1 del; 7 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8748.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8748/head:pull/8748

PR: https://git.openjdk.java.net/jdk/pull/8748