wpe-2.38 Improve memory usage during GCHeap snapshot

[asurdej-comcast]

This is kind of improvement for GC heap snapshot generation that prints the snapshot directly to file instead keeping it all in json string (and then print into file). This helps to reduce memory usage spike that was required for huge json string and also eliminates a crash caused by string size limit exceed.

I think it can be useful for WPE, embedded case when memory is limited, not sure if suitable for upstream webkit repo.
With this patch I'm able to dump pretty big GC heap into file without getting OOM from kernel

The second change is to allow different dir for heap snapshot. With containers enabled /tmp space is limited usually so better to use other location, vendor specific

0
__libc_do_syscall
‎:
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__pthread_kill_implementation
‎/usr/src/debug/glibc/2.35-r0/git/nptl/pthread_kill.c:43
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raise
‎/usr/src/debug/glibc/2.35-r0/git/signal/../sysdeps/posix/raise.c:26
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abort
‎/usr/src/debug/glibc/2.35-r0/git/stdlib/abort.c:79
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void WTF::StringBuilder::allocateBuffer
‎/usr/src/debug/wpe-webkit/2.38.8+gitAUTOINC+d893a3ed1d-r1/build/../git/Source/WTF/wtf/text/StringBuilder.cpp:46
5
WTF::StringBuilder::extendBufferForAppendingWithUpconvert
‎/usr/src/debug/wpe-webkit/2.38.8+gitAUTOINC+d893a3ed1d-r1/build/../git/Source/WTF/wtf/text/StringBuilder.cpp:144
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WTF::StringBuilder::appendQuotedJSONString
‎/usr/src/debug/wpe-webkit/2.38.8+gitAUTOINC+d893a3ed1d-r1/build/../git/Source/WTF/wtf/text/StringBuilderJSON.cpp:98
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JSC::HeapSnapshotBuilder::json
‎/usr/src/debug/wpe-webkit/2.38.8+gitAUTOINC+d893a3ed1d-r1/build/../git/Source/JavaScriptCore/heap/HeapSnapshotBuilder.cpp:552
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JSC::HeapSnapshotBuilder::json
‎/usr/src/debug/wpe-webkit/2.38.8+gitAUTOINC+d893a3ed1d-r1/build/../git/Source/JavaScriptCore/heap/HeapSnapshotBuilder.cpp:308
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WebCore::GCController::dumpHeap
‎/usr/src/debug/wpe-webkit/2.38.8+gitAUTOINC+d893a3ed1d-r1/build/../git/Source/WebCore/bindings/js/GCController.cpp:162
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_g_cclosure_marshal_VOID__OBJECT_OBJECT_ENUMv
‎/usr/src/debug/glib-2.0/1_2.72.3-r0/build/../glib-2.72.3/gio/gmarshal-internal.c:1380
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_g_closure_invoke_va
‎/usr/src/debug/glib-2.0/1_2.72.3-r0/build/../glib-2.72.3/gobject/gclosure.c:893
12
g_signal_emit_valist
‎/usr/src/debug/glib-2.0/1_2.72.3-r0/build/../glib-2.72.3/gobject/gsignal.c:3406
13
g_signal_emit
‎/usr/src/debug/glib-2.0/1_2.72.3-r0/build/../glib-2.72.3/gobject/gsignal.c:3553
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g_file_monitor_emit_event
‎/usr/src/debug/glib-2.0/1_2.72.3-r0/build/../glib-2.72.3/gio/gfilemonitor.c:294
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https://github.com/WebPlatformForEmbedded/WPEWebKit/commit/38ae47ceffb7a2c00e24cf59c26bdcd55ff434e4

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