Summary
-------

Make `TrimNativeHeapInterval` a product switch

Problem
-------

JDK-8293114 introduced automatic C-heap trimming, for now supported only by the glibc. It is controlled by the command line switch `TrimNativeHeapInterval`. 
The feature has proven to be very valuable to customers, and all issues have been ironed out. Therefore, I propose to make this switch a non-experimental
product switch.

Solution
--------

The solution is to remove the EXPERIMENTAL moniker from this switch.

In addition to that, the `java` man page will be changed to mention this option as well as its limitation to Linux glibc-based systems.

In addition to that, a release note will be written.

Specification
-------------

```
--- a/src/hotspot/share/runtime/globals.hpp
+++ b/src/hotspot/share/runtime/globals.hpp
@@ -1996,7 +1996,7 @@ const int ObjectAlignmentInBytes = 8;
           "2: monitors & new lightweight locking (LM_LIGHTWEIGHT)")         \
           range(0, 2)                                                       \
                                                                             \
-  product(uint, TrimNativeHeapInterval, 0, EXPERIMENTAL,                    \
+  product(uint, TrimNativeHeapInterval, 0,                                  \
           "Interval, in ms, at which the JVM will trim the native heap if " \
           "the platform supports that. Lower values will reclaim memory "   \
           "more eagerly at the cost of higher overhead. A value of 0 "      \
```