fix: documentation for custom parsing

Documentation for `custom<X>` in `assemblyFormat` used the wrong return type. See `parsePrettyLLVMType()` in LLVMTypes.h, `parseSingleBlockRegion()` in IRDL.cpp, `parseDynamicIndexList()` in ViewLikeInterface.cpp, etc.

Author: tim-hoffman

mlir/docs/DefiningDialects/AttributesAndTypes.md

@@ -890,7 +890,7 @@ The `custom` directive `custom<Foo>($foo)` will in the parser and printer
 respectively generate calls to:
 
 ```c++
-LogicalResult parseFoo(AsmParser &parser, int &foo);
+ParseResult parseFoo(AsmParser &parser, int &foo);
 void printFoo(AsmPrinter &printer, int foo);
 ```
 
@@ -907,7 +907,7 @@ let assemblyFormat = "custom<Fizz>($foobar)";
 It will generate calls expecting the following signature for `parseFizz`:
 
 ```c++
-LogicalResult parseFizz(AsmParser &parser, FailureOr<NotDefaultConstructible> &foobar);
+ParseResult parseFizz(AsmParser &parser, FailureOr<NotDefaultConstructible> &foobar);
 ```
 
 A previously bound variable can be passed as a parameter to a `custom` directive
@@ -916,7 +916,7 @@ the first directive. The second directive references it and expects the
 following printer and parser signatures:
 
 ```c++
-LogicalResult parseBar(AsmParser &parser, int &bar, int foo);
+ParseResult parseBar(AsmParser &parser, int &bar, int foo);
 void printBar(AsmPrinter &printer, int bar, int foo);
 ```
 
@@ -925,7 +925,7 @@ is that the parameter for the parser must use the storage type of the parameter.
 For example, `StringRefParameter` expects the parser and printer signatures as:
 
 ```c++
-LogicalResult parseStringParam(AsmParser &parser, std::string &value);
+ParseResult parseStringParam(AsmParser &parser, std::string &value);
 void printStringParam(AsmPrinter &printer, StringRef value);
 ```