SceneView : Add default name to plugs for setting up attribute queries
SceneView : Add default name to plugs for setting up attribute queries

- Works around MSVC bug :
    k:\build\gaffer\include\gaffer\numericplug.h(60): fatal error C1001: An internal error has occurred in the compiler.
    (compiler file 'msc1.cpp', line 1518)
    To work around this problem, try simplifying or changing the program near the locations listed above.
    Please choose the Technical Support command on the Visual C++
    Help menu, or open the Technical Support help file for more information
    Internal Compiler Error in C:\Program Files (x86)\Microsoft Visual Studio\2017\Community\VC\Tools\MSVC\14.16.27023\bin\HostX64\x64\cl.exe.  You will be prompted to send an error report to Microsoft later.
    INTERNAL COMPILER ERROR in 'C:\Program Files (x86)\Microsoft Visual Studio\2017\Community\VC\Tools\MSVC\14.16.27023\bin\HostX64\x64\cl.exe'

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