Expose parseXInDimensionList() to the `DialectAsmParser`

[mehdi_amini]

Summary

This allows custom types and attribute to parse a dimension list that
isn't necessarily terminated with xtype, for example something like:

#tf.shape<4x5>

[rriddle]

mlir/include/mlir/IR/DialectImplementation.h

366

Can you rephrase element type to something like "jutxtaposed with an identifier" or something?

mlir/include/mlir/IR/DialectImplementation.h

public:
   ///   dimension-list ::= (dimension `x`)*
   ///   dimension ::= `?` | integer
   ///
   /// When `allowDynamic` is not set, this is used to parse:
   ///
   ///   static-dimension-list ::= (integer `x`)*
   virtual ParseResult parseDimensionList(SmallVectorImpl<int64_t> &dimensions,
                                          bool allowDynamic = true) = 0;
+
+  /// Parse an 'x' token in a dimension list, handling the case where the x is
+  /// juxtaposed with an element type, as in "xf32", leaving the "f32" as the
+  /// next token.
+  virtual ParseResult parseXInDimensionList() = 0;
 };
 
 } // end namespace mlir
 
 #endif

mlir/lib/Parser/DialectSymbolParser.cpp

ParseResult parseType(Type &result) override {
     return success(static_cast<bool>(result));
   }
 
   ParseResult parseDimensionList(SmallVectorImpl<int64_t> &dimensions,
                                  bool allowDynamic) override {
     return parser.parseDimensionListRanked(dimensions, allowDynamic);
   }
 
+  ParseResult parseXInDimensionList() override {
+    return parser.parseXInDimensionList();
+  }
+
   OptionalParseResult parseOptionalType(Type &result) override {
     return parser.parseOptionalType(result);
   }
 
 private:
   /// The full symbol specification.
   StringRef fullSpec;