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/ElementWiseUnaryFixture.h b/tests/validation/fixtures/ElementWiseUnaryFixture.h
index b1d54fd..26484be 100644
--- a/tests/validation/fixtures/ElementWiseUnaryFixture.h
+++ b/tests/validation/fixtures/ElementWiseUnaryFixture.h
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2018-2020 Arm Limited.
+ * Copyright (c) 2018-2021 Arm Limited.
  *
  * SPDX-License-Identifier: MIT
  *
@@ -76,7 +76,7 @@
                 {
                     case DataType::F16:
                     {
-                        arm_compute::utils::uniform_real_distribution_fp16 distribution{ half(-2.0f), half(2.0f) };
+                        arm_compute::utils::uniform_real_distribution_fp16 distribution{ -2.0f, 2.0f };
                         library->fill(tensor, distribution, i);
                         break;
                     }