2squash: Increase received images size limit to 35 Mpx

+ Rename it to MAX_RCVD_IMAGE_PIXELS to make it clear that sending isn't affected.
+ Add a doc comment.

Author: iequidoo

src/constants.rs

@@ -193,8 +193,9 @@ pub(crate) const WORSE_AVATAR_BYTES: usize = 20_000; // this also fits to Outloo
 pub const BALANCED_IMAGE_SIZE: u32 = 1280;
 pub const WORSE_IMAGE_SIZE: u32 = 640;
 
-// Limit displayed images ~8.3 megapixels (3840 × 2160)
-pub const MAX_IMAGE_PIXELS: u32 = 8294400;
+/// Limit for received images size. Bigger images become `Viewtype::File` to avoid excessive memory
+/// usage by UIs.
+pub const MAX_RCVD_IMAGE_PIXELS: u32 = 35_000_000;
 
 // Key for the folder configuration version (see below).
 pub(crate) const DC_FOLDERS_CONFIGURED_KEY: &str = "folders_configured";

src/mimeparser.rs

@@ -1386,7 +1386,7 @@ impl MimeMessage {
         {
             match get_filemeta(decoded_data) {
                 // image size is known, not too big, keep msg_type:
-                Ok((width, height)) if width * height <= constants::MAX_IMAGE_PIXELS => {
+                Ok((width, height)) if width * height <= constants::MAX_RCVD_IMAGE_PIXELS => {
                     part.param.set_i64(Param::Width, width.into());
                     part.param.set_i64(Param::Height, height.into());
                     msg_type