patch 9.1.2022: using C++ keyword class as member variable name

patch 9.1.2022: using C++ keyword class as member variable name

Problem:  A recent commit introduced a member variable named `class` in
          the `exarg` structure, which conflicts with the C++ keyword
          `class`. This causes compilation issues on Windows when VIM
          is compiled with OLE enabled, as "if_ole.cpp" cannot compile
          due to the keyword conflict (after v9.1.2012).
Solution: Rename the member variable of `exarg` from `class` to `ea_class`.
          (Wei Tang)

related: #18949
closes:  #19016

Signed-off-by: Wei Tang <gauchyler@uestc.edu.cn>
Signed-off-by: Christian Brabandt <cb@256bit.org>