Use filebase64 for launch template userdata and Terraform 0.12

[rifelpet]

In order to provide the HCL2 generation code with knowledge of which function to use for each file reference (file() vs filebase64() we need to store that in the Literal, so this adds a new field with that information.

Fixes #9518

[k8s-ci-robot]

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[rifelpet]

/cc @fred-vogt

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[fred-vogt]

@rifelpet - I can confirm this fixes the issue for me with a build of your branch.

[hakman]

/lgtm