Add new texture filtering "Auto Max Quality" that tweaks texture filtering for best quality.

It does this by enforcing mipmapping and minification filters, and
always autogenerates mipmaps and enforces anisotropic filtering for all
modes (if that's separately enabled).

This looks nice and flicker free in most games without any additional
tweaking, including GTA and Burnout which have long been painfully
flickery in the distance due to undersampling.

Needs a bit more testing before merge, maybe.

Fixes #13888

GPU/Vulkan/TextureCacheVulkan.cpp

@@ -751,6 +751,15 @@ void TextureCacheVulkan::BuildTexture(TexCacheEntry *const entry) {
 	// such as when using replacement textures - but let's keep the same amount of levels.
 	int maxLevelToGenerate = maxLevel;
 
+	if (g_Config.iTexFiltering == TEX_FILTER_AUTO_MAX_QUALITY) {
+		// Boost the number of mipmaps.
+		int maxPossibleMipmaps = log2i(std::min(gstate.getTextureWidth(0), gstate.getTextureHeight(0)));
+		if (maxPossibleMipmaps != maxLevelToGenerate) {
+			maxLevelToGenerate = maxPossibleMipmaps;
+		}
+	}
+
+
 	// If GLES3 is available, we can preallocate the storage, which makes texture loading more efficient.
 	VkFormat dstFmt = GetDestFormat(GETextureFormat(entry->format), gstate.getClutPaletteFormat());