Fix non-determinism in material shader maps.

Fixed:
- certain uninitialized fields
- non-deterministic name sorting in memory images

#rb Ben.Ingram (original CLs)
#jira none
#lockdown Cristina.Riveron

(Edigrating CLs 14347633, 14428640 from UE4-Main to Release-4.26)

#ROBOMERGE-OWNER: Arciel.Rekman
#ROBOMERGE-AUTHOR: arciel.rekman
#ROBOMERGE-SOURCE: CL 14677770 in //UE4/Release-4.26/...
#ROBOMERGE-BOT: RELEASE (Release-4.26 -> Release-Engine-Staging) (v756-14651656)
#ROBOMERGE-CONFLICT from-shelf

[CL 14677926 by Arciel Rekman in Release-Engine-Staging branch]

Engine/Shaders/Public/ShaderVersion.ush

@@ -3,4 +3,4 @@
 // in Platform.ush (which should be included in any shader) it allows to invalidate the shader DDC.
 // 
 // If you are merging streams and there is a conflict with this GUID you should make a new GUID rather than taking one or the other.
-// GUID = C8A4AAC4-97AE-42A5-8468-AADC357FC814
+// GUID = 4558FB11-3241-43D9-B708-A2D3250DF1F5

Engine/Source/Runtime/Engine/Private/ShaderDerivedDataVersion.h

@@ -10,5 +10,5 @@
 
 // In case of merge conflicts with DDC versions, you MUST generate a new GUID and set this new
 // guid as version
-#define GLOBALSHADERMAP_DERIVEDDATA_VER			TEXT("CE4A26A5071E4C9596A658A9AC69B29B")
-#define MATERIALSHADERMAP_DERIVEDDATA_VER		TEXT("9147101451524D13ACE72CCECEC5F230")
+#define GLOBALSHADERMAP_DERIVEDDATA_VER			TEXT("8C01E9655F2D469DB664C8E826EBA0BD")
+#define MATERIALSHADERMAP_DERIVEDDATA_VER		TEXT("01BF92A5B29A44BE8A839E4251DA49D7")