feat: initial `r/gh` realm #1534

Job	Run time
build (1.20.x, GOARCH=amd64 GOOS=linux, gno)	47s
build (1.20.x, GOARCH=wasm GOOS=js, gno)	41s
build (1.21.x, GOARCH=amd64 GOOS=linux, gno)	37s
test (1.20.x, _test.cmd)	1m 24s
build (1.21.x, GOARCH=wasm GOOS=js, gno)	35s
test (1.20.x, _test.pkg)	1m 10s
test (1.20.x, _test.gnolang.native)	59s
test (1.20.x, _test.gnolang.stdlibs)	1m 52s
test (1.20.x, _test.gnolang.realm)	1m 18s
test (1.20.x, _test.gnolang.pkg0)	2m 53s
test (1.20.x, _test.gnolang.pkg1)	8m 2s
test (1.20.x, _test.gnolang.pkg2)	5m 36s
test (1.20.x, _test.gnolang.other)	1m 1s
test (1.21.x, _test.cmd)	1m 47s
test (1.21.x, _test.pkg)	1m 37s
test (1.21.x, _test.gnolang.native)	1m 5s
test (1.21.x, _test.gnolang.stdlibs)	1m 49s
test (1.21.x, _test.gnolang.realm)	1m 2s
test (1.21.x, _test.gnolang.pkg0)	2m 18s
test (1.21.x, _test.gnolang.pkg1)	10m 16s
test (1.21.x, _test.gnolang.pkg2)	5m 32s
test (1.21.x, _test.gnolang.other)	50s
	53m 11s

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