[LV] Emit all remarks for unvectorizable instructions (#153833)

If ExtraAnalysis is requested, emit all remarks caused by unvectorizable instructions - instead of only the first.
This is in line with how other places handle DoExtraAnalysis and it can be quite helpful to get info about all instructions in a loop that prevent vectorization.

Author: tobias-stadler

llvm/include/llvm/Transforms/Vectorize/LoopVectorizationLegality.h

@@ -493,6 +493,9 @@ class LoopVectorizationLegality {
   /// and we only need to check individual instructions.
   bool canVectorizeInstrs();
 
+  /// Check if an individual instruction is vectorizable.
+  bool canVectorizeInstr(Instruction &I);
+
   /// When we vectorize loops we may change the order in which
   /// we read and write from memory. This method checks if it is
   /// legal to vectorize the code, considering only memory constrains.