Inline compiler warnings and errors

**I propose we** add `#warning` and `#error` [from C#](https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/preprocessor-directives#error-and-warning-information)

Given we have `#line` already for code generation scenarios, we should also support inline warning and error messages to further support code generation scenarios. Compared to C#'s preprocessor directives `#warning` and `#error`, an even better way to support this without necessitating parser changes would be two compiler intrinsics called `warning` and `error` which are functions that take a string and return a unit, to be added to FSharp.Core. An additional check would be needed to ensure that the string passed in is a compile-time constant though. Doing this would further allow multi-line messages easily unlike C#'s preprocessor directives.
```fs
let workInProgress() =
warning "Work in progress" // Generates a warning by using the warning function in FSharp.Core
1
let generatedStub() = error "Implement this" // Generates an error by using the error function in FSharp.Core
```

**The existing way of approaching this problem in F# is**
```fs
let [] warning = ()
let workInProgress() =
warning // Generates a warning
1
let [] error = ()
let generatedStub() = error // Generates an error
```
However, attributes can't always be used at a local `let`, e.g. within a local function, leading to a huge distance between definition and usage. Moreover, the definition and usage must be separated, which is undesirable for use-once messages.

## Pros and Cons

**The advantages of making this adjustment to F# are**
1. Better support for marking WIP code and generated stubs to be implemented
2. Clarity of intent

**The disadvantage of making this adjustment to F# is** one more thing to learn.

## Extra information

**Estimated cost (XS, S, M, L, XL, XXL):** S

**Related suggestions:**
- https://github.com/fsharp/fslang-suggestions/issues/90
It might also be worthwhile to add
```fs
[]
[]
let inline tba<'a> : 'a = raise(NotImplementedException("To be added"))
```
To FSharp.Core too.

## Affidavit (please submit!)

Please tick these items by placing a cross in the box:
* [x] This is not a question (e.g. like one you might ask on [StackOverflow](http://stackoverflow.com)) and I have searched StackOverflow for discussions of this issue
* [x] This is a language change and not purely a tooling change (e.g. compiler bug, editor support, warning/error messages, new warning, non-breaking optimisation) belonging to [the compiler and tooling repository](https://github.com/dotnet/fsharp)
* [x] This is not something which has obviously "already been decided" in previous versions of F#. If you're questioning a fundamental design decision that has obviously already been taken (e.g. "Make F# untyped") then please don't submit it
* [x] I have [searched both open and closed suggestions on this site](http://github.com/fsharp/fslang-suggestions/issues) and believe this is not a duplicate

Please tick all that apply:
* [x] This is not a breaking change to the F# language design
* [x] I or my company would be willing to help implement and/or test this

## For Readers

If you would like to see this issue implemented, please click the :+1: emoji on this issue. These counts are used to generally order the suggestions by engagement.

No implementation files, tests, or entry points are named. Start by reviewing the proposed F# intrinsics and related suggestion #90; determine whether compiler directives or FSharp.Core functions are intended, with done defined as compile-time-constant messages producing warnings or errors in local functions and generated code.

Written by the indexing model from the issue text.