Rename demangle to mat_demangle to avoid boost name conflict (#1479) #248

Job	Run time
Linux (x64-linux)	5m 11s
macOS (native)	2m 29s
Windows (x64-windows-static)	4m 33s
iOS (arm64-ios cross-compile)	2m 14s
Android (arm64-v8a API 23 cross-compile)	4m 56s
	19m 23s

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