Rename ANGLE libs in order to not conflict with other ANGLE libs

This is needed to be able to use Qt (with dynamic ANGLE) in a plugin
while the host runs a different version of Qt (and ANGLE).

In addition to changing the LIBEGL_NAME and LIBGLESV2_NAME variables
you also need to update the value of the LIBRARY definition in the
.def files for ANGLE:

    qtbase/src/3rdparty/angle/src/libGLESv2/libGLESv2[d?].def
    qtbase/src/3rdparty/angle/src/libGLESv2/libEGL[d?].def

Task-number: QTBUG-48431
Change-Id: Idd00d039ba3e20cc0ec7496bee36ed1c90383b0d
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@theqtcompany.com>