Anisotropic Filtering: Anisotropic is not supported for the mip filter

[CookiePLMonster]

D3DTEXF_ANISOTROPIC cannot be used with D3DSAMP_MIPFILTER. This is backed by multiple other pages:

1. D3DTEXTUREFILTERTYPE enumeration states that using D3DTEXF_ANISOTROPIC with the mip filter is undefined.
2. There is no D3DPTFILTERCAPS entry to test for anisotropic with the mip filter.

One more potentially important point, based on my own recent mistake: The mag filter technically supports Anisotropic, but in practice D3DPTFILTERCAPS_MAGFANISOTROPIC is false on most modern hardware and ignoring that might lead to problems (my application's rendering broke due to me missing this point). Should maybe this page be updated to remind the user to check for D3DPTFILTERCAPS_MAGFANISOTROPIC and D3DPTFILTERCAPS_MINFANISOTROPIC before using the filter, to avoid mistakes like mine?

[prmerger-automator]

@CookiePLMonster : Thanks for your contribution! The author(s) and reviewer(s) have been notified to review your proposed change.