fix(sdk): update loop dsl to handle same argument in nested loop

[Tomcli]

Which issue is resolved by this Pull Request: Resolves #1045

Description of your changes: The original loop dsl only returns the original argument name no matter the loop is nested or not, updating loop dsl to handle same argument in nested loops.

Environment tested:

• Python Version (use python --version):
• Tekton Version (use tkn version):
• Kubernetes Version (use kubectl version):
• OS (e.g. from /etc/os-release):

Checklist:

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[Tomcli]

cc @Udiknedormin I have to change the way how the dsl name the argument in order to fix this issue. Let me know if you see any problem with this approach.

[Tomcli]

@ScrapCodes for the sdk/python/tests/compiler/testdata/nested_loop_same_arg.yaml example, the pipeline loop cache hit triggered despite the argument is different in the next nested loop. I think your caching logic was based on the spec and and argument name, but the nested loop could have the same argument name but passing down a different value. So we may need a better way to check for this edge case as well.

[google-oss-prow[bot]]

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This pull-request has been approved by: Tomcli, yhwang

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