feat: add Swift codes for chapter_searching articles

[nuomi1]

If this PR is related to coding or code translation, please fill out the checklist.

• I've tested the code and ensured the outputs are the same as the outputs of reference codes.
• I've checked the codes (formatting, comments, indentation, file header, etc) carefully.
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1 Ignored Deployment

Name	Status	Preview	Comments	Updated
hello-algo	⬜️ Ignored (Inspect)			Jan 29, 2023 at 11:57AM (UTC)

[nuomi1]

result of `linear_search.swift`

目标元素 3 的索引 = 2
目标结点值 3 的对应结点对象为 utils.ListNode

result of `binary_search.swift`

目标元素 6 的索引 = 2
目标元素 6 的索引 = 2

result of `hashing_search.swift`

目标元素 3 的索引 = 2
目标结点值 3 的对应结点对象为 utils.ListNode

[krahets]

Thanks for the PR!