[bug] Fix dictContentType when reprocessing cdict

Conditions to trigger:
* CDict is loaded as raw content.
* CDict starts with the zstd dictionary magic number.
* The CDict is reprocessed (not attached or copied).
* The new API is used (streaming or `ZSTD_compress2()`).

Bug: The dictionary is loaded as a zstd dictionary, not a raw content
dictionary, because the dict content type is set to `ZSTD_dct_auto`.

Fix: Pass in the dictionary content type from cdict creation to the call
to `ZSTD_compress_insertDictionary()`.

Test: Added a test case that exposes the bug, and fixed the raw
content tests to not modify the `dictBuffer`, which makes all future
tests with the `dictBuffer` raw content, which doesn't seem intentional.

lib/compress/zstd_compress.c

@@ -64,6 +64,7 @@ size_t ZSTD_compressBound(size_t srcSize) {
 struct ZSTD_CDict_s {
     const void* dictContent;
     size_t dictContentSize;
+    ZSTD_dictContentType_e dictContentType; /* The dictContentType the CDict was created with */
     U32* entropyWorkspace; /* entropy workspace of HUF_WORKSPACE_SIZE bytes */
     ZSTD_cwksp workspace;
     ZSTD_matchState_t matchState;
@@ -3188,7 +3189,7 @@ static size_t ZSTD_compressBegin_internal(ZSTD_CCtx* cctx,
                 ZSTD_compress_insertDictionary(
                         cctx->blockState.prevCBlock, &cctx->blockState.matchState,
                         &cctx->ldmState, &cctx->workspace, &cctx->appliedParams, cdict->dictContent,
-                        cdict->dictContentSize, dictContentType, dtlm,
+                        cdict->dictContentSize, cdict->dictContentType, dtlm,
                         cctx->entropyWorkspace)
               : ZSTD_compress_insertDictionary(
                         cctx->blockState.prevCBlock, &cctx->blockState.matchState,
@@ -3460,6 +3461,7 @@ static size_t ZSTD_initCDict_internal(
         ZSTD_memcpy(internalBuffer, dictBuffer, dictSize);
     }
     cdict->dictContentSize = dictSize;
+    cdict->dictContentType = dictContentType;
 
     cdict->entropyWorkspace = (U32*)ZSTD_cwksp_reserve_object(&cdict->workspace, HUF_WORKSPACE_SIZE);