Add documentation for and!/applicative computation expressions

[baronfel]

F# 5 added support for applicative Computation Expressions via the and! syntax, and it should be documented here.

Useful Links:

• preview announcement
• Language RFC
• Note from Don Syme about applicatives

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Document Details

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• ID: 247c440d-b855-0df1-f2db-076cd3393a0b
• Version Independent ID: 1cbccd4d-1721-e14f-7546-8fa868c965b1
• Content: Computation Expressions - F#
• Content Source: docs/fsharp/language-reference/computation-expressions.md
• Product: dotnet-fsharp
• GitHub Login: @cartermp
• Microsoft Alias: dotnetcontent

[mducharm]

Hello, I'm new to contributing, please let me know if there's anything I can improve - thanks!

[gewarren]

Fixed by #30447.