RFR: 8360884: Better scoped values [v5]

[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 one additional commit since the last revision:

  Little things.

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/26019/files
  - new: https://git.openjdk.org/jdk/pull/26019/files/f8ff2965..c87e8367

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=26019&range=04
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=26019&range=03-04

  Stats: 6 lines in 1 file changed: 2 ins; 0 del; 4 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