Specializations for type `string` for `Chunk` and `SlidingWindow`

[FreeApophis]

Chunk and SlidingWindow on a string return arrays of char. It would be nice to have specific overloads which return strings instead.

"abcdefghij".StringChunk(3) would returns "abc", "def", "ghi" "j"

"abcdef".StringSlidingWindows(3) would returns "abc", "bcd", "cde" "def"

• Names open for discussion

[FreeApophis]

Idea: Chunk on string @ sharplab