message: Add dialect-attribute-entry requirement to docs
  This commit add `dialect-attribute-entry` requirements on function arguments,
  function results, and function attributes to the documentation.
diff: @@ -343,6 +343,9 @@ some other module) has no body. While the MLIR textual form provides a nice
  inline syntax for function arguments, they are internally represented as "block
  arguments" to the first block in the region.
  +Only dialect attribute names may be specified in the attribute dictionaries for
  +function arguments, results, or the function itself.
  +
  Examples:
  ```mlir {.mlir}
  @@ -355,6 +358,15 @@ func @count(%x: i64) -> (i64, i64)
  attributes {fruit: "banana"} {
  return %x, %x: i64, i64
  }
  +
  +// A function with an argument attribute
  +func @example_fn_arg(%x: i32 {swift.self = unit})
  +
  +// A function with a result attribute
  +func @example_fn_result() -> (f64 {dialectName.attrName = 0 : i64})
  +
  +// A function with an attribute
  +func @example_fn_attr() attributes {dialectName.attrName = false}
  ```
  ## Blocks
  @@ -1422,8 +1434,8 @@ either is the self/context or it isn't.
  ```mlir {.mlir}
  // A unit attribute defined with the `unit` value specifier.
  -func @verbose_form(i1) attributes {unitAttr = unit}
  +func @verbose_form(i1) attributes {dialectName.unitAttr = unit}
  // A unit attribute can also be defined without the value specifier.
  -func @simple_form(i1) attributes {unitAttr}
  +func @simple_form(i1) attributes {dialectName.unitAttr}
  ```
  