(fix)[flatten-array]: Enable Flattening of all nested arrays in the array

[superhit0]

Fixes: #564

Algorithm:

- Loop over depth till depth becomes 0
 - if in any iteration the depth > 0 but array does not contain any array as its element, then break
 - Iterate over the current array and if the current element is not an array, simply push it to next stack otherwise unwrap the array of one depth and then push the unwrapped array into next stack array

Dry Run:

Input Sample 1:
Input Array = [[1, [2, 3], 4], [5, [6, [7, [8]]]]];
Depth = 6;
Result = [1, 2, 3, 4, 5, 6, 7, 8];

Depth	Array At Start of Iteration	Array At End of Iteration
6	[[1, [2, 3], 4], [5, [6, [7, [8]]]]]	[1, [2, 3], 4, 5, [6, [7, [8]]]]
5	[1, [2, 3], 4, 5, [6, [7, [8]]]]	[1, 2, 3, 4, 5, 6, [7, [8]]]
4	[1, 2, 3, 4, 5, 6, [7, [8]]]	[1, 2, 3, 4, 5, 6, 7, [8]]
3	[1, 2, 3, 4, 5, 6, 7, [8]]	[1, 2, 3, 4, 5, 6, 7, 8]
2	[1, 2, 3, 4, 5, 6, 7, 8]	[1, 2, 3, 4, 5, 6, 7, 8]
1	[1, 2, 3, 4, 5, 6, 7, 8] (break Due to Array containing no array)

Input Sample 2:
Input Array = [[1, [2, 3], 4], [5, [6, [7, [8]]]]];
Depth = 3;
Result = [1, 2, 3, 4, 5, 6, 7, [8]];

Depth	Array At Start of Iteration	Array At End of Iteration
3	[[1, [2, 3], 4], [5, [6, [7, [8]]]]]	[1, [2, 3], 4, 5, [6, [7, [8]]]]
2	[1, [2, 3], 4, 5, [6, [7, [8]]]]	[1, 2, 3, 4, 5, 6, [7, [8]]]
1	[1, 2, 3, 4, 5, 6, [7, [8]]]	[1, 2, 3, 4, 5, 6, 7, [8]]
0	[1, 2, 3, 4, 5, 6, 7, [8]] (break Due to depth === 0)

[superhit0]

@angus-c please let me know your thoughts on this PR. Thanks.