[mlir][Linalg] Fix formatting of generated docs markdown

[benmxwl-arm]

Summary

This patch prevents mlir-linalg-ods-yaml-gen from adding extra
whitespace around the summary and description fields. This broke the
_italics_ of the summary as _ this _ is not recognised by markdown.
It also meant the first line of the description was in a code block

as it was indented two spaces.

The separator between summary and description has also been updated to
two newlines. This was already followed and prevents line wrapping the
summary putting part of it in the description.

These issues can be currently seen at: https://mlir.llvm.org/docs/Dialects/Linalg/

[benmxwl-arm]

• Allow line wrapping the summary
• Rebase

[awarzynski]

I've been meaning to fix this for ages, thank you :) LGTM

mlir/include/mlir/Dialect/Linalg/IR/LinalgNamedStructuredOps.yaml

value: !ScalarExpression
                 type_var: AccumType
                 operands:
                 - !ScalarExpression
                   scalar_arg: rhs
 --- !LinalgOpConfig
 metadata: !LinalgOpMetadata
   name: batch_mmt4d
   cpp_class_name: BatchMmt4DOp
-  doc: "Performs a batched matrix-matrix-transpose multiplication of two\nbatched-4D\
-    \ (5D) inputs.\n\nBesides the outermost batch dimension has the same semantic\
-    \ as\nlinalg.batch_matmul, the differences from linalg.batch_matmul in the\nnon-batch\
-    \ dimensions are the same as linalg.mmt4d vs. linalg.matmul. See the\ndescription\
-    \ of lingalg.mmt4d."
+  doc: |-
+    Performs a batched matrix-matrix-transpose multiplication of two batched-4D
+    (5D) inputs.
+
+    Besides the outermost batch dimension has the same semantic as
+    linalg.batch_matmul, the differences from linalg.batch_matmul in the
+    non-batch dimensions are the same as linalg.mmt4d vs. linalg.matmul. See the
+    description of lingalg.mmt4d.
   implements:
   - LinalgContractionOpInterface
 structured_op: !LinalgStructuredOpConfig
   args:
   - !LinalgOperandDefConfig
     name: lhs
     kind: input_tensor
     type_var: LhsType

mlir/test/mlir-linalg-ods-gen/test-linalg-ods-yaml-gen.yaml

value: !ScalarExpression
             attr_name: cast
             type_var: T
             operands:
             - !ScalarExpression
               scalar_index: 1
 
 # ODS-LABEL:  def Test1Op : LinalgStructuredBase_Op<"test1"
 
-#       ODS:  let summary = [{ Title. }];
-#  ODS-NEXT:  let description = [{
-#  ODS-NEXT:    Detailed description.
-#  ODS-NEXT:  }];
+#       ODS:  let summary = [{Title.}];
+#  ODS-NEXT:  let description = [{Detailed description.}];
 
 #       ODS:  let arguments =
 #  ODS-NEXT:    Variadic<AnyType>:$inputs,
 #  ODS-NEXT:    Variadic<AnyShaped>:$outputs,
 #  ODS-NEXT:    DefaultValuedOptionalAttr<TypeFnAttr, "TypeFn::cast_signed">:$cast
 
 #       ODS:  let builders =
 #       ODS:  (ins "TypeRange":$resultTensorTypes, "ValueRange":$inputs,

mlir/tools/mlir-linalg-ods-gen/mlir-linalg-ods-yaml-gen.cpp

static LogicalResult generateNamedGenericOpOds(LinalgOpConfig &opConfig,
   std::string interfaceNameList;
   std::string attrList;
   std::string attrMethods;
   std::string attrBuilder;
 
   std::string doc;
   if (opConfig.metadata->doc) {
     static const char structuredOpDocFmt[] = R"FMT(
-  let summary = [{ {0} }];
-  let description = [{
-    {1}
-  }];
+  let summary = [{{{0}}];
+  let description = [{{{1}}];
 )FMT";
     StringRef summary, description;
     std::tie(summary, description) =
-        StringRef(*opConfig.metadata->doc).trim().split('\n');
+        StringRef(*opConfig.metadata->doc).trim().split("\n\n");
+
     doc = llvm::formatv(structuredOpDocFmt, summary.trim(), description.trim());
   }
 
   interfaceNameList = interleaveToString(opConfig.metadata->implements, ", ");
 
   std::string definitionList;
   for (const std::string &definition : opConfig.metadata->defines) {
     static const char definitionFmt[] = "let {0} = 1;\n";