Add new lints: const_sized_chunks_exact, const_sized_chunks_exact_mut, and const_sized_windows

[immersum]

Suggests using array_chunks and array_windows (Closes #6580)

These methods are nightly-only, so the lints have been added to nursery

changelog: new lint: [const_sized_chunks_exact]
changelog: new lint: [const_sized_chunks_exact_mut]
changelog: new lint: [const_sized_windows]

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[immersum]

In the three lints, the suggestions are as follows:

• .chunks_exact(n) → .array_chunks()
• .chunks_exact_mut(n) → .array_chunks_mut()
• .windows(n) → .array_windows()

Right now, there are three lints declared for the three methods:

• [const_sized_chunks_exact]
• [const_sized_chunks_exact_mut]
• [const_sized_windows]

Question 1. Do you think it would be better to reduce the number of lints to just two?

• [const_sized_chunks_exact] – would include the checks for the _mut method
• [const_sized_windows]

Question 2. Do you think it would be even better to reduce that number to just one?

• [const_sized_chunks] – would include the checks for all three methods: chunks_exact, chunks_exact_mut, and windows
  Note: There are two feature gates: array_chunks and array_windows