allow named fields in active patterns

I'm trying to use a library which exposes active patterns instead of the data types with their internal definition.

https://github.com/fsprojects/FSharp.Data/blob/8a6688f34abede0a80306e6c802601ef74edf473/src/FSharp.Data.Html.Core/HtmlActivePatterns.fs

The experience isn't as good as direct access to the representation, but it could be improved:

I suggest we allow active patterns to define field names:

```fsharp
module HtmlActivePatterns =
let (|HtmlElement(name,attributes,elements)|HtmlText(content)|HtmlComment(content)|HtmlCData(content)|) (node: HtmlNode) =
match node with
| HtmlNode.HtmlText content -> HtmlText(content)
| HtmlNode.HtmlComment content -> HtmlComment(content)
| HtmlNode.HtmlCData content -> HtmlCData(content)
| HtmlNode.HtmlElement (name, attributes, elements) -> HtmlElement(name, attributes, elements)
```

Here, I defined the field names explicitly (this is just a suggested syntax).

Possibly, if those aren't defined, but the value given is a plain identifier like in the code above, it would put the equivalent of `nameof identifier` for the name.

Possibly, we would issue a warning (on by default in new projects), when the names are not defined.

If we don't want to change the representation, we may make this work like C# value tuple with names work.

https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/builtin-types/value-tuples#tuple-field-names

The deconstruction syntax would allow partial deconstruction, using the usual syntax with explicit field names instead of positional one.

We may also allow the constructor syntax to specify the names (and have a check that enforces consistency):

```fsharp
module HtmlActivePatterns =
let (|HtmlElement|HtmlText|HtmlComment|HtmlCData|) (node: HtmlNode) =
match node with
| HtmlNode.HtmlText content -> HtmlText(content=content)
| HtmlNode.HtmlComment content -> HtmlComment(content=content)
| HtmlNode.HtmlCData content -> HtmlCData(content=content)
| HtmlNode.HtmlElement (name, attributes, elements) -> HtmlElement(name=name, attributes=attributes, elements=elements)
```

Start with the linked FSharp.Data HtmlActivePatterns.fs example and the issue's proposed active-pattern and C# value-tuple field-name syntax. No implementation files or tests are named; done would require an agreed syntax and semantics for named fields, plus corresponding compiler changes and tests.

Written by the indexing model from the issue text.