fix(gnolang): make Go2Gno return a prespective error instead of sudden/elusive runtime panic with a bad receiver

[odeke-em]

The pattern:

func() A()

confuses Go into expecting a receiver and it returns a compile time error "missing receiver", but previously Gno panicked with a runtime error due to a deference yet the Recv.List was empty. This change fixes that by detecting that condition and prescriptively panicking which can then be relayed reasonably as expecting to the calling user.

Fixes #3727

[Gno2D2]

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[codecov]

Codecov Report

Attention: Patch coverage is 66.66667% with 1 line in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
gnovm/pkg/gnolang/go2gno.go	66.66%	1 Missing ⚠️

📢 Thoughts on this report? Let us know!

[thehowl]

Let's go for filetests to test behaviour of the GnoVM functions on full Gno files.

I modified the two panics to match Go's error as I think they're more intelligible.

It seems that panics out of Go2Gno do not have line information; that's something you could look to add :)

[odeke-em]

Thank you @thehowl for the commits and sounds good, thank you!