nGraph 'shell' implementation for GatherElements-6 and MO 'shell' implementation (#3467)

* Initial support of GatherElements in MO and nGraph

* apply_style

* added lost extractor for GatherElements

* Corrected GatherElements::validate_and_infer_types

* updated package_BOM.txt

* Type_t added

* started to implement ngraph shape_type_infer unit-tests

* finally implemented all ngraph shape_inference unit-tests

* updated Supported_Frameworks_Layers.md

* added correct handling of dynamic shapes in nGraph, added unit-tests for dynamic cases, fixed dump typos in MO, replaced axis type from int -> int64_t

* implemented shape infer for dynamic shapes with intervals

* finalized MO implementation

* applied comment from review

* style-apply

* spec correction

* removed conflict

* fixed typos

* removed obsolete comments form type_prop

* significant corrections in validate_and_infer_types

* style-apply

* data_rank check for axis

docs/MO_DG/prepare_model/Supported_Frameworks_Layers.md

@@ -338,6 +338,7 @@ Standard ONNX\* operators:
 | Floor | No |
 | GRU | No |
 | Gather | No |
+| GatherElements | Doesn't work with negative indices |
 | GatherND | No |
 | GatherTree | No |
 | Gemm | No |

docs/ops/movement/GatherElements_6.md

@@ -20,53 +20,53 @@ For instance, in the 3D case (`r = 3`), the output is determined by the followin
 ```
 Example 1 with concrete values:
 ```
-  data = [
-      [1, 2],
-      [3, 4],
-  ]
-  indices = [
-      [0, 1],
-      [0, 0],
-  ]
-  axis = 0
-  output = [
-        [1, 4],
-        [1, 2],
-  ]
+data = [
+    [1, 2],
+    [3, 4],
+]
+indices = [
+    [0, 1],
+    [0, 0],
+]
+axis = 0
+output = [
+    [1, 4],
+    [1, 2],
+]
 ```
 Example 2 with `axis` = 1 and `indices` having greater (than `data`) shape:
 ```
 data = [
-      [1, 7],
-      [4, 3],
-  ]
-  indices = [
-      [1, 1, 0],
-      [1, 0, 1],
-  ]
-  axis = 1
-  output = [
-        [7, 7, 1],
-        [3, 4, 3],
-  ]
+    [1, 7],
+    [4, 3],
+]
+indices = [
+    [1, 1, 0],
+    [1, 0, 1],
+]
+axis = 1
+output = [
+    [7, 7, 1],
+    [3, 4, 3],
+]
 ```
 
 Example 3 `indices` has lesser (than `data`) shape:
 ```
 data = [
-      [1, 2, 3],
-      [4, 5, 6],
-      [7, 8, 9],
-  ]
-  indices = [
-      [1, 0, 1],
-      [1, 2, 0],
-  ]
-  axis = 0
-  output = [
-        [4, 2, 6],
-        [4, 8, 3],
-  ]
+    [1, 2, 3],
+    [4, 5, 6],
+    [7, 8, 9],
+]
+indices = [
+    [1, 0, 1],
+    [1, 2, 0],
+]
+axis = 0
+output = [
+    [4, 2, 6],
+    [4, 8, 3],
+]
 ```
 
 **Attributes**: