common : relax sampler name matching (#23744)

* common : relax sampler name matching

Currently, in some cases, the alternative names for samplers (like
`top-k` and `min-p` instead of the canonical `top_k` and `min_p`) are
not always recognized by the `common_sampler_types_from_names` function
in `common/sampling.cpp`.

This PR changes the signature of this function to remove the `bool
allow_alt_names` flag, and removes all occurences of the flag from call
sites. Therefore, the function will now always match all known names.

I also changed the logic of the function to unconditionally check the
provided sampler names against both the canonical and alternative names,
and to be case-insensitive.

This fixes an issue I was seeing wherein samplers specified in the
`llama-server` UI were not recognized as valid when the alternative
names were used.

* add more alt names

* cont. fix

* cast to unsigned char for correctness

* common : unify sampler name mapping

* annotate canonical vs. alt sampler name mappings per @CISC

* Update common/sampling.cpp

Co-authored-by: Sigbjørn Skjæret <sigbjorn.skjaeret@scala.com>

* common : auto-generate sampler name aliases per @ngxson

* use merged map for matching

* use `.merge` instead of iterating

* nit: simplify comment

* nit: use insert everywhere, not index assignment

---------

Co-authored-by: Sigbjørn Skjæret <sigbjorn.skjaeret@scala.com>

common/common.cpp

@@ -1148,7 +1148,7 @@ static void common_init_sampler_from_model(
         if (llama_model_meta_val_str(model, llama_model_meta_key_str(LLAMA_MODEL_META_KEY_SAMPLING_SEQUENCE), buf, sizeof(buf)) > 0) {
             const std::vector<std::string> sampler_names = string_split<std::string>(std::string(buf), ';');
             if (!sampler_names.empty()) {
-                sparams.samplers = common_sampler_types_from_names(sampler_names, true);
+                sparams.samplers = common_sampler_types_from_names(sampler_names);
             }
         }
     }