proposal.String() panics with nested Anys

[amaury1093]

Summary of Bug

When calling .String() on a proto struct that has nested Anys, it panics. A quick debugging leads to the field any.cachedValue panicking.

panic: reflect.Value.Interface: cannot return value obtained from unexported field or method

see stack

It seems to me that gogoproto panics when printing our Any's cachedValue.

ref: #10868 (comment)

Version

8f13e99

Steps to Reproduce

cosmos-sdk/x/gov/types/v1beta2/proposals_test.go

Lines 31 to 42 in 8f13e99

	// TestNestedAnys tests that we can call .String() on a struct with nested Anys.
	// Here, we're creating a proposal which has a Msg (1st any) with a legacy
	// content (2nd any).
	func TestNestedAnys(t *testing.T) {
	testProposal := v1beta1.NewTextProposal("Proposal", "testing proposal")
	msgContent, err := v1beta2.NewLegacyContent(testProposal, "cosmos1govacct")
	require.NoError(t, err)
	proposal, err := v1beta2.NewProposal([]sdk.Msg{msgContent}, 1, time.Now(), time.Now())
	require.NoError(t, err)
	require.Equal(t, "TODO Fix panic here", proposal.String())
	}

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[fdymylja]

This needs to be fixed in regen proto fork I assume.

[julienrbrt]

When we fix this, does that mean we are able to rely on String()?
And thus do not need this: https://github.com/cosmos/cosmos-sdk/blob/main/docs/docs/core/05-encoding.md#custom-stringer (see #12908)