[SPEC] Clarify specification for StridedSlice

[PiotrKrzem]

Details:

• Add notes with descriptions of: Out of Bounds, Indexing in Reverse, Negative Indices
• Clarified length of masks
• Clarified the definition of -1 value
• Described in detail the behavior of masks, aligned with Reference Implementation

TODO:

• Add more latex-like style, add the examples for the missing masks.

Tickets:

• 90128