mtmd: Add Gemma3n multimodal support with MobileNetV5 vision encoder (#18256)

* Add Gemma3nVisionModel - MobileNetV5 vision encoder convertor to convert_hf_to_gguf.py. Add gemma3n to vision projectors in gguf-py/gguf/constants.py.

* Add mobilenetv5 impl

* Fix comments, remove unused vars

* Fix permute and remove transpose of projection weights

* Fix comments, remove debugging prints from hf_to_gguf

* 1. Hard-code image_mean = 0 and image_std = 1
2. Use available tensor mapping logic
3. Remove redundant chat template replacement of soft tokens placeholder with media placeholder

* 1. Move mobilenetv5 helpers declarations to `clip_graph_mobilenetv5` struct and definitions to mobilenetv5.cpp
2.Remove unused `clip_is_gemma3n` func declarations and definitions
3. Remove redundant `rescale_image_u8_to_f32` func and use `normalize_image_u8_to_f32` with zero mean and unit std
4. Calculate n_patches using image_size / patch_size

* Remove obsolete comments

* - convert_hf_to_gguf.py & constants.py & tensor_mapping.py: Use explicit mapping: Custom map for double indexed blocks and tensor_mapping.py for rest
- convert_hf_to_gguf.py: Unsqueeze Stem Bias and Layer scale tensors to correct shape while converting to gguf
- mobilenetv5.cpp: Remove explicit reshaping of Stem Bias and Layer scale which are now handled while converting to gguf, replace fprintf with LOG_*
- clip.cpp: Remove unused embedding and hard_emb_norm tensor loading

* - Rename tensors to v.conv..., v.blk..., v.msfa... to better align with already existing terminology

* Fix stem conv bias name

* Remove explicit handling of bias term for stem conv

* - Change order of addition in "project_per_layer_inputs" to support broadcasting of vision inp_per_layer
- Simplify the vision embeddings path of "get_per_layer_inputs" to output [n_embd_altup, n_layer, 1], broadcastable

* clean up conversion script

* fix code style

* also preserve audio tensors

* trailing space

* split arch A and V

* rm unused gemma3 func

* fix alignment

---------

Co-authored-by: Xuan Son Nguyen <son@huggingface.co>

tools/mtmd/mtmd.cpp

@@ -266,7 +266,7 @@ struct mtmd_context {
         }
 
         // set boi/eoi
-        if (proj == PROJECTOR_TYPE_GEMMA3) {
+        if (proj == PROJECTOR_TYPE_GEMMA3 || proj == PROJECTOR_TYPE_GEMMA3NV) {
             // <start_of_image> ... (image embeddings) ... <end_of_image>
             img_beg = "<start_of_image>";
             img_end = "<end_of_image>";
@@ -862,10 +862,15 @@ float * mtmd_get_output_embd(mtmd_context * ctx) {
 }
 
 bool mtmd_decode_use_non_causal(mtmd_context * ctx) {
-    if (ctx->ctx_v && clip_get_projector_type(ctx->ctx_v) == PROJECTOR_TYPE_GEMMA3) {
-        return true;
+    switch (ctx->proj_type_v()) {
+        case PROJECTOR_TYPE_QWEN2VL:
+        case PROJECTOR_TYPE_QWEN25VL:
+        case PROJECTOR_TYPE_QWEN3VL:
+        case PROJECTOR_TYPE_YOUTUVL:
+            return true;
+        default:
+            return false;
     }
-    return false;
 }
 
 bool mtmd_decode_use_mrope(mtmd_context * ctx) {