k8s_yaml handles string yaml poorly

repro:
make a 1-line tiltfile with k8s_yaml(str(local('kustomize build https://github.com/kubernetes-sigs/cluster-api//config/default?ref=v0.2.5')))
(Note this is a bad Tiltfile - the str should not be there. I wrote this while mistakenly thinking I needed to convert my blob to a string to pass it to k8s_yaml)

observed:
fsevent errors that screw up the terminal

expected:
not that

This is handled here.

Basically, absPathFromStarlarkValue happily converts this huge yaml string into an absolute path, and then we try to open it and set up watches on it, and then apparently fsevents generate terminal-destroying log messages when it get bad paths?

So maybe there are a couple things here:

1. fsevents errors shouldn't garble the terminal
2. We've talked about inferring string vs blob - it'd be nice to give a better error message here. (even ignoring #1, the log ends up being so much yaml that you can't see the start of the log, and then a "filename too long", and it's not super clear what happened)

Reproduce the issue with the one-line Tiltfile, then inspect internal/tiltfile/k8s.go around the linked line and the absPathFromStarlarkValue path. Done means the malformed string no longer produces terminal-destroying filesystem errors and the resulting diagnostic makes the misuse clear.