perf: optimize Gvk.ApiVersion()

[ephesused]

Convert Gvk.ApiVersion() from using strings.Builder to raw string concatenation. The logic in Gvk.ApiVersion() is simple enough that raw concatenation executes quicker and consumes less memory.

This commit provides performance improvements that help the code flow prior to OpenAPI parsing, #4569.

For the current master branch, the new benchmark test shows:

$ go test ./kyaml/resid -bench=BenchmarkApiVersion -benchmem -run='^$'
goos: windows
goarch: amd64
pkg: sigs.k8s.io/kustomize/kyaml/resid
cpu: Intel(R) Core(TM) i7-7700 CPU @ 3.60GHz
BenchmarkApiVersion/0-8         199093560                5.821 ns/op           0 B/op          0 allocs/op
BenchmarkApiVersion/1-8         49935914                25.02 ns/op            8 B/op          1 allocs/op
BenchmarkApiVersion/2-8         37500937                29.12 ns/op            8 B/op          1 allocs/op
BenchmarkApiVersion/3-8         44452182                27.99 ns/op            8 B/op          1 allocs/op
BenchmarkApiVersion/4-8         45229936                29.36 ns/op            8 B/op          1 allocs/op
BenchmarkApiVersion/5-8         16000682                67.16 ns/op           48 B/op          2 allocs/op
PASS
ok      sigs.k8s.io/kustomize/kyaml/resid       8.565s

For this commit, the new benchmark test shows:

$ go test ./kyaml/resid -bench=BenchmarkApiVersion -benchmem -run='^$'
goos: windows
goarch: amd64
pkg: sigs.k8s.io/kustomize/kyaml/resid
cpu: Intel(R) Core(TM) i7-7700 CPU @ 3.60GHz
BenchmarkApiVersion/0-8         892631328                1.388 ns/op           0 B/op          0 allocs/op
BenchmarkApiVersion/1-8         884411148                1.356 ns/op           0 B/op          0 allocs/op
BenchmarkApiVersion/2-8         55792155                21.04 ns/op            0 B/op          0 allocs/op
BenchmarkApiVersion/3-8         57150204                21.14 ns/op            0 B/op          0 allocs/op
BenchmarkApiVersion/4-8         60002700                21.23 ns/op            0 B/op          0 allocs/op
BenchmarkApiVersion/5-8         55470295                22.03 ns/op            0 B/op          0 allocs/op
PASS
ok      sigs.k8s.io/kustomize/kyaml/resid       8.322s

[k8s-ci-robot]

Hi @ephesused. Thanks for your PR.

I'm waiting for a kubernetes-sigs member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

Once the patch is verified, the new status will be reflected by the ok-to-test label.

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[KnVerey]

/ok-to-test
/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: ephesused, KnVerey

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