Add merge slots to Bignum files

Legacy Bignum is excluded as it doesn't get regular extensions like new
ones.

Each slot uses comments of their respective filetype. Since .data files
don't have a syntax for comments, dummy test cases are used. (These test
cases will never be executed and no noise will be added to tests.)

Signed-off-by: Janos Follath <janos.follath@arm.com>

scripts/mbedtls_dev/bignum_core.py

@@ -815,3 +815,44 @@ def mpi_modmul_case_generate() -> None:
             )
             i += 1
     print(generated_inputs)
+
+# BEGIN MERGE SLOT 1
+
+# END MERGE SLOT 1
+
+# BEGIN MERGE SLOT 2
+
+# END MERGE SLOT 2
+
+# BEGIN MERGE SLOT 3
+
+# END MERGE SLOT 3
+
+# BEGIN MERGE SLOT 4
+
+# END MERGE SLOT 4
+
+# BEGIN MERGE SLOT 5
+
+# END MERGE SLOT 5
+
+# BEGIN MERGE SLOT 6
+
+# END MERGE SLOT 6
+
+# BEGIN MERGE SLOT 7
+
+# END MERGE SLOT 7
+
+# BEGIN MERGE SLOT 8
+
+# END MERGE SLOT 8
+
+# BEGIN MERGE SLOT 9
+
+# END MERGE SLOT 9
+
+# BEGIN MERGE SLOT 10
+
+# END MERGE SLOT 10
+