RFR: 8309390: [JVMCI] improve copying system properties into libgraal [v2]

[Doug Simon]

> This PR improves the startup time for libgraal by speeding up how `VM.savedProps` is copied into libgraal. This data structure is now serialized to a native buffer directly from C++ and the native buffer is then directly decoded by libgraal.
> 
> ## Times
> 
> The basic benchmarking below shows that this change brings the time for a nop Java app with eager libgraal initialization (2) down to almost the same time as lazy libgraal initialization (1). The latter typically means no libgraal initialization happens as a top tier JIT compilation is never scheduled in such a short running app.
> 
> 
> public class Nop {
>     public static void main(String[] args) {}
> }
> 
> 
> (1) Baseline (no options):
> 
>> for i in (seq 10); java Nop; end
>         0.05 real         0.04 user         0.01 sys
>         0.04 real         0.03 user         0.01 sys
>         0.04 real         0.03 user         0.01 sys
>         0.04 real         0.03 user         0.01 sys
>         0.03 real         0.03 user         0.00 sys
>         0.04 real         0.03 user         0.01 sys
>         0.04 real         0.03 user         0.00 sys
>         0.03 real         0.03 user         0.00 sys
>         0.04 real         0.03 user         0.01 sys
>         0.03 real         0.03 user         0.00 sys
> 
> 
> (2) Eagerly initialize libgraal (with PR):
> 
>> for i in (seq 10); /usr/bin/time java -XX:+EagerJVMCI Nop; end
>         0.06 real         0.04 user         0.01 sys
>         0.05 real         0.03 user         0.01 sys
>         0.05 real         0.03 user         0.01 sys
>         0.05 real         0.03 user         0.01 sys
>         0.05 real         0.03 user         0.01 sys
>         0.05 real         0.03 user         0.01 sys
>         0.05 real         0.03 user         0.01 sys
>         0.05 real         0.03 user         0.01 sys
>         0.05 real         0.03 user         0.01 sys
>         0.05 real         0.03 user         0.01 sys
> 
> 
> (3) Eagerly initialize libgraal (without PR):
> 
>> for i in (seq 10); /usr/bin/time java -XX:+EagerJVMCI Nop; end
>         0.11 real         0.08 user         0.02 sys
>         0.08 real         0.06 user         0.01 sys
>         0.08 real         0.07 user         0.01 sys
>         0.10 real         0.07 user         0.01 sys
>         0.08 real         0.06 user         0.01 sys
>         0.10 real         0.07 user         0.01 sys
>         0.08 real         0.07 user         0.01 sys
>         0.08 real         0.07 user         0.01 sys
>         0.08 real         0.06 user         0.01 sys
>         0.08 real  ...

Doug Simon has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains two commits:

 - [skip ci] snapshot Arguments::system_properties() in JVMCI instead of System.savedProps
 - more efficient copying of system properties into libjvmci

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

Changes: https://git.openjdk.org/jdk/pull/14291/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=14291&range=01
  Stats: 277 lines in 17 files changed: 103 ins; 89 del; 85 mod
  Patch: https://git.openjdk.org/jdk/pull/14291.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14291/head:pull/14291

PR: https://git.openjdk.org/jdk/pull/14291