Enhance blacklisting to allow for specifying files by extension

[Lewis Rosenthal]

Currently, classes/c/c_common/som_and_wps.c defines the following INI keys to allow skipping file scanning:

#define MM_INVALID_DRIVES      "mmClsDontCheckDrives"
#define MM_INVALID_ID3DRIVES   "mmClsDontReadID3OnDrives"

This RFE proposes adding:

#define MM_INVALID_TYPES       "mmClsDontReadTypesOnDrives"

which would allow for adding a comma-separated list of file extensions to be ignored, even when encountered on drives not listed in mmClsDontCheckDrives, e.g.:

mp3,flac,ogg,avi

Alternatively, or in addition, we could exclude based on EA information, but this seems somewhat unreliable to me. It is highly unlikely to encounter an MPEG4 video file with a .txt extension, though it may be necessary to list multiple possible extension strings (mpeg4,mp4) for the same type. There are also filesystems which are incapable of properly retaining EAs, and such metadata may not be present.

Reference: ​Arca Noae #0001599: Slow loading of media content of USB disk, SMB folder.