fix: Fix subArray and substring while index equals the length of array/string

[Danieladu]

Fixes #3616

Description

It should be valid in function subArray and substring while index equals to the length of Array/String.
For example:
subArray([1], 1, 1) should return []
substring('ab', 2, 0) should return empty string

Tag: The substring part should be port to C#

[coveralls]

Pull Request Test Coverage Report for Build 815441815

• 2 of 2 (100.0%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.003%) to 85.434%

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Totals
Change from base Build 811247959:	-0.003%
Covered Lines:	19217
Relevant Lines:	21393

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💛 - Coveralls

[joshgummersall]

@Danieladu what's the status of this?