feat: add p/demo/svg (#905) #11

Job	Run time
build (1.19.x, amd64, linux, ./cmd/tm2txsync)	28s
build (1.19.x, amd64, linux, ./pkg/amino/cmd/aminoscan)	33s
build (1.19.x, amd64, linux, ./pkg/amino/cmd/goscan)	13s
build (1.19.x, amd64, linux, ./pkg/autofile/cmd)	16s
build (1.19.x, amd64, linux, ./pkg/iavl/cmd/iaviewer)	17s
build (1.20.x, amd64, linux, ./cmd/tm2txsync)	37s
build (1.20.x, amd64, linux, ./pkg/amino/cmd/aminoscan)	21s
build (1.20.x, amd64, linux, ./pkg/amino/cmd/goscan)	16s
build (1.20.x, amd64, linux, ./pkg/autofile/cmd)	18s
build (1.20.x, amd64, linux, ./pkg/iavl/cmd/iaviewer)	22s
test (1.19.x, _test.flappy)	42s
test (1.19.x, _test.pkg.amino)	3m 53s
test (1.19.x, _test.pkg.bft)	4m 34s
test (1.19.x, _test.pkg.others)	4m 48s
test (1.19.x, _test.cmds)	37s
test (1.20.x, _test.flappy)	1m 1s
test (1.20.x, _test.pkg.amino)	3m 51s
test (1.20.x, _test.pkg.bft)	15m 14s
test (1.20.x, _test.pkg.others)	5m 24s
test (1.20.x, _test.cmds)	1m 5s
	44m 50s

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