Fix the symbol filter not working in the mapping view

[LagoLunatic]

Fixes #311

[dbalatoni13]

I just noticed that now when you enter the symbol mapping view while you have a filter, the filter stays there on the other side. I think we might need considerations about this because you usually want to search for something and then map to something different, right?

[LagoLunatic]

I just noticed that now when you enter the symbol mapping view while you have a filter, the filter stays there on the other side. I think we might need considerations about this because you usually want to search for something and then map to something different, right?

Updated so that the mapping filter is stored separately. I also cleared the mapping filter when switching between views, so the mapping filter won't be preserved across mapping two different functions, it will always be blank when you start mapping to avoid confusion. But the regular non-mapping filter is still preserved when switching views.

(By the way, it seems the version of objdiff on decomp.me already had the behavior of the filter being shared between mapping and non-mapping. Not sure how to modify that one though.)

[dbalatoni13]

Sounds great, going to test it right away

[tomsons26]

Works as intended