RFR: 8286331: jni_GetStringUTFChars() uses wrong heap allocator

[Zhengyu Gu]

jni_GetStringUTFChars()  calls `AllocateHeap(length + 1, mtInternal, 0, AllocFailStrategy::RETURN_NULL);` to allocate memory, where it passes `0` as `NativeCallStack` reference, that results construction of `NativeCallStack`.

In `NativeCallStack`'s constructor, it performs stack walk to capture native call stack. This is unnecessary, if NMT detail tracking is not enabled.

It should use `char* AllocateHeap(size_t size,
                   MEMFLAGS flags,
                   AllocFailType alloc_failmode /* = AllocFailStrategy::EXIT_OOM*/)` heap allocator instead.

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Commit messages:
 - v0

Changes: https://git.openjdk.java.net/jdk/pull/8579/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8579&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8286331
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8579.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8579/head:pull/8579

PR: https://git.openjdk.java.net/jdk/pull/8579