Weighted votes migrate in-place migrations

[amaury1093]

Description

ref: #8345 (comment)
closes #8345

---

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[amaury1093]

In v040 we had

type Vote struct {
	ProposalId uint64           `protobuf:"varint,1,opt,name=proposal_id,json=proposalId,proto3" json:"proposal_id,omitempty" yaml:"proposal_id"`
	Voter      string           `protobuf:"bytes,2,opt,name=voter,proto3" json:"voter,omitempty"`
	Option     types.VoteOption `protobuf:"varint,3,opt,name=option,proto3,enum=cosmos.gov.v1beta1.VoteOption" json:"option,omitempty"`
}

and in v042 we add a new field, and marked the 3rd field as reserved, which gives

type Vote struct {
	ProposalId uint64               `protobuf:"varint,1,opt,name=proposal_id,json=proposalId,proto3" json:"proposal_id,omitempty" yaml:"proposal_id"`
	Voter      string               `protobuf:"bytes,2,opt,name=voter,proto3" json:"voter,omitempty"`
	Options    []WeightedVoteOption `protobuf:"bytes,4,rep,name=options,proto3" json:"options"`
}

Here, I went through the old .pb.go and copy-pasted the minimum to have the old vote struct and its proto marshaling working.

[lgtm-com]

This pull request introduces 1 alert when merging c5f4d03 into 0e24bad - view on LGTM.com

new alerts:

• 1 for Useless assignment to local variable

[codecov]

Codecov Report

Merging #8663 (7104ee0) into master (a193522) will decrease coverage by 0.03%.
The diff coverage is 27.50%.

@@            Coverage Diff             @@
##           master    #8663      +/-   ##
==========================================
- Coverage   61.44%   61.41%   -0.04%     
==========================================
  Files         673      674       +1     
  Lines       38361    38399      +38     
==========================================
+ Hits        23571    23581      +10     
- Misses      12309    12335      +26     
- Partials     2481     2483       +2     

Impacted Files	Coverage Δ
x/gov/keeper/migrations.go	50.00% <0.00%> (ø)
x/gov/legacy/v040/vote.go	0.00% <0.00%> (ø)
x/gov/legacy/v042/store.go	84.61% <73.33%> (-15.39%)	⬇️

[robert-zaremba]

LGTM