[foreign-memaccess+abi] RFR: Avoid using StandardCharset in Java code [v2]

[Per Minborg]

> According to a comment in `java.nio.charset.StandardCharsets`, the use of this class should be avoided from elsewhere in the `jdk.base` module. This PR proposes removing all such direct use of said class in Java code (but not in JavaDocs).
> 
> 
> public final class StandardCharsets {
> 
>     // To avoid accidental eager initialization of often unused Charsets
>     // from happening while the VM is booting up, which may delay
>     // initialization of VM components, we should generally avoid depending
>     // on this class from elsewhere in java.base.

Per Minborg has updated the pull request incrementally with two additional commits since the last revision:

 - Remove benchmark
 - Use a faster if rake

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

Changes:
  - all: https://git.openjdk.org/panama-foreign/pull/864/files
  - new: https://git.openjdk.org/panama-foreign/pull/864/files/954d3162..4a844ac0

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=panama-foreign&pr=864&range=01
 - incr: https://webrevs.openjdk.org/?repo=panama-foreign&pr=864&range=00-01

  Stats: 17 lines in 1 file changed: 8 ins; 1 del; 8 mod
  Patch: https://git.openjdk.org/panama-foreign/pull/864.diff
  Fetch: git fetch https://git.openjdk.org/panama-foreign.git pull/864/head:pull/864

PR: https://git.openjdk.org/panama-foreign/pull/864