RFR: 8360884: Better scoped values [v4]

[Andrew Haley]

> Scoped values cannot be used early in the JDK boot process because of some dependencies on System.getProperty(). This dependency should be removed in a way that allows scoped values to be created (but not necessarily bound) at any stage during boot.
> 
> Also, Scoped Value's constructor has a synchronized block, which limits the use of scoped values at runtime. Constructing a scoped value should be a thread-local operation.

Andrew Haley has updated the pull request incrementally with two additional commits since the last revision:

 - 8360884: Better scoped values
 - 8360884: Better scoped values

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/26019/files
  - new: https://git.openjdk.org/jdk/pull/26019/files/3f01aad6..f8ff2965

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=26019&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=26019&range=02-03

  Stats: 30 lines in 2 files changed: 9 ins; 13 del; 8 mod
  Patch: https://git.openjdk.org/jdk/pull/26019.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/26019/head:pull/26019

PR: https://git.openjdk.org/jdk/pull/26019