[jdk11u-dev] RFR: 8268893: jcmd to trim the glibc heap

[Thomas Stuefe]

Backport the System.trim_native_heap command to 11.

This needs a CSR backport, which exists, it was approved for 11 ages ago (https://bugs.openjdk.org/browse/JDK-8273602) but then the actual backport fell under the table.

The downport is not clean. Since [8282382](https://bugs.openjdk.org/browse/JDK-8282382) had been downported selectively, which introduced `print_glibc_malloc_tunables` to os_linux.cpp, which sits smack in the middle of the code to change. The hunk affected breaks out the proc-file-reading from the old `os::Linux::print_process_memory_info()` into `os::Linux::query_process_memory_info()` - with this patch, both functions are identical now between jdk11u and later releases even though the diff looks different.

Patch was tested in GHAs, and I ran manual tests with `jcmd .. System.trim_native_heap`, all works.

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Commit messages:
 - Backport 6096dd9765eaf280890f65c0ff1ab64864b9316a

Changes: https://git.openjdk.org/jdk11u-dev/pull/1354/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk11u-dev&pr=1354&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8268893
  Stats: 267 lines in 6 files changed: 236 ins; 21 del; 10 mod
  Patch: https://git.openjdk.org/jdk11u-dev/pull/1354.diff
  Fetch: git fetch https://git.openjdk.org/jdk11u-dev pull/1354/head:pull/1354

PR: https://git.openjdk.org/jdk11u-dev/pull/1354