[llvm] [docs][CMake] Add CMakePreset, improve VS documentation (PR #84760)

[James Henderson via llvm-commits]

================
@@ -0,0 +1,89 @@
+
+/*
+   This is the default presets for LLVM, if you want to add your own
+   custom one, create a CMakeUserPreset.json instead.
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jh7370 wrote:

```suggestion
   custom one, create a CMakeUserPresets.json instead.
```

https://github.com/llvm/llvm-project/pull/84760