test: add reverseiterator tests #1348

Job	Run time
build (1.19.x, GOARCH=amd64 GOOS=linux, gno)	43s
build (1.19.x, GOARCH=wasm GOOS=js, gno)	40s
build (1.20.x, GOARCH=amd64 GOOS=linux, gno)	44s
build (1.20.x, GOARCH=wasm GOOS=js, gno)	43s
test (1.19.x, _test.cmd)	1m 12s
test (1.19.x, _test.pkg)	59s
test (1.19.x, _test.gnolang.native)	43s
test (1.19.x, _test.gnolang.stdlibs)	1m 42s
test (1.19.x, _test.gnolang.realm)	58s
test (1.19.x, _test.gnolang.pkg0)	2m 11s
test (1.19.x, _test.gnolang.pkg1)	9m 7s
test (1.19.x, _test.gnolang.pkg2)	5m 29s
test (1.19.x, _test.gnolang.other)	40s
test (1.20.x, _test.cmd)	1m 29s
test (1.20.x, _test.pkg)	1m 11s
test (1.20.x, _test.gnolang.native)	55s
test (1.20.x, _test.gnolang.stdlibs)	1m 30s
test (1.20.x, _test.gnolang.realm)	57s
test (1.20.x, _test.gnolang.pkg0)	2m 17s
test (1.20.x, _test.gnolang.pkg1)	8m 19s
test (1.20.x, _test.gnolang.pkg2)	7m 12s
test (1.20.x, _test.gnolang.other)	1m 5s
	50m 46s

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