Fix uniform_real_distribution_fp16 warning and single Dimension increment

- Change uniform_real_distribution_fp16's arguments to float to avoid maybe-uninitialized warnings in half data type's copy constructor and converter
- Add increment method to Dimensions in order to avoid possible overflows when incrementing single dimensions
- Remove internal_only flag documentation

Resolves: COMPMID-4061

Change-Id: I7c50487193bd7b47b03d52fc595840c7df4e7104
Signed-off-by: Giorgio Arena <giorgio.arena@arm.com>
Reviewed-on: https://review.mlplatform.org/c/ml/ComputeLibrary/+/4760
Reviewed-by: Georgios Pinitas <georgios.pinitas@arm.com>
Tested-by: Arm Jenkins <bsgcomp@arm.com>
Comments-Addressed: Arm Jenkins <bsgcomp@arm.com>
diff --git a/tests/validation/fixtures/GEMMLowpFixture.h b/tests/validation/fixtures/GEMMLowpFixture.h
index 338cf01..b9140eb 100644
--- a/tests/validation/fixtures/GEMMLowpFixture.h
+++ b/tests/validation/fixtures/GEMMLowpFixture.h
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2017-2020 Arm Limited.
+ * Copyright (c) 2017-2021 Arm Limited.
  *
  * SPDX-License-Identifier: MIT
  *
@@ -79,7 +79,7 @@
         }
         case DataType::F16:
         {
-            arm_compute::utils::uniform_real_distribution_fp16 distribution{ half(-1.0f), half(1.0f) };
+            arm_compute::utils::uniform_real_distribution_fp16 distribution{ -1.0f, 1.0f };
             library->fill(tensor, distribution, i);
             break;
         }