[wasm][coreclr] Make fcalls follow the new calling convention

[radekdoulik]

We will need update fcalls to follow https://github.com/dotnet/runtime/blob/main/docs/design/coreclr/botr/clr-abi.md#outgoing-call-abi

Context: #123215 (comment) #121215

/cc @kg @AndyAyersMS

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