[llvm] [Tablegen] Add keywork `dump`. (PR #68793)

[Francesco Petrogalli via llvm-commits]

================
@@ -1275,6 +1275,23 @@ be nested.
 This loop defines records named ``R0``, ``R1``, ``R2``, and ``R3``, along
 with ``F0``, ``F1``, ``F2``, and ``F3``.
 
+``dump`` --- print messages to stderr
+-------------------------------------
+
+A ``dump`` statement prints the input string to standard error
+output. It is intended for debugging purpose.
+
+.. productionlist::
+   Dump: "dump"  `string` ";"
+
+For example, it can be used in combination with `!repl` to investigate
----------------
fpetrogalli wrote:

```suggestion
For example, it can be used in combination with `!repr` to investigate
```

https://github.com/llvm/llvm-project/pull/68793