Fix binary search to return first occurrence when duplicates exist

[ANIKET640-a11y]

Describe your change:

Fixes #13840

• Add an algorithm?
• Fix a bug or typo in an existing algorithm?
• Add or change doctests? -- Note: Please avoid changing both code and tests in a single pull request.
• Documentation change?

Modified the binary_search() implementation so that when duplicate elements exist in a sorted collection, the function returns the index of the first occurrence instead of an arbitrary occurrence.

Checklist:

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• This PR only changes one algorithm file. To ease review, please open separate PRs for separate algorithms.
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