Improve wasm errors

[wleese]

Currently WASM compiled functions panic when attempting to return an error.
Also, the error returned is often not meaningful without retrieving the resourceList.Results and showing them to the user.

This change builds on this PR GoogleContainerTools/kpt-functions-catalog#978 to benefit from the additional function, introduced to allow retrieving and showing resourceList.Results to the user.
Both that and this PR should solve #3822.

Shortcomings:

1. No effort is made to match resourceList.Results entries to the entry introduced by the last function. In the PR I assume that entries with Severity "error" result in the function failing, and that all "error" entries are relevant
2. ...

Previously, output would be like this:

➜ KPT_FN_WASM_RUNTIME=nodejs kpt fn render . --allow-alpha-wasm --allow-exec
Package "kpt2":
[RUNNING] WASM "starlark-wasm"
[FAIL] "starlark-wasm" in 800ms
Error: wrong Node Kind for  expected: MappingNode was ScalarNode: value: {undefined}


➜ kpt fn render . --allow-alpha-wasm --allow-exec
Package "kpt2":
[RUNNING] WASM "starlark-wasm"
panic: ValueOf: invalid value

goroutine 6 [running]:
syscall/js.ValueOf({0xf46c0, 0x1653560})
	/opt/local/lib/go/src/syscall/js/js.go:208 +0xf7
syscall/js.Value.Set({{}, 0x7ff8000100000012, 0x15b0690}, {0x2017f8, 0x6}, {0xf46c0, 0x1653560})
	/opt/local/lib/go/src/syscall/js/js.go:303 +0x8
syscall/js.handleEvent()
	/opt/local/lib/go/src/syscall/js/func.go:95 +0x27
[FAIL] "starlark-wasm" in 0s
Error: invalid resource list output from wasm library; got "s(<nil>"

With these changes, including the PR for the functions:

➜  KPT_FN_WASM_RUNTIME=nodejs kpt fn render . --allow-alpha-wasm --allow-exec
Package "kpt2":
[RUNNING] WASM "starlark-wasm"
[FAIL] "starlark-wasm" in 500ms
Error: wrong Node Kind for  expected: MappingNode was ScalarNode: value: {key "params" not in dict}

➜  kpt fn render . --allow-alpha-wasm --allow-exec
Package "kpt2":
[RUNNING] WASM "starlark-wasm"
[FAIL] "starlark-wasm" in 0s
Error: parsing output resource list with content: "unable to process resource list: error: function failure"
yaml: mapping values are not allowed in this context
&{key "params" not in dict}

The key message here is key "params" not in dict, as in my example I had a starlark function that tries to access params when it is not available.

[mortent]

Maybe use a more descriptive name here than err2?

[wleese]

I gave it another shot.

[natasha41575]

Thanks so much for working on this and for providing more detailed context and investigation in the issue as well. This is a great change. I have some small nits below.

One last thing, could you update the PR description to add what the error output looked like before, and what this PR changes it to? (So that someone without context can immediately understand the behavior change.)

[natasha41575]

LGTM. Will defer to @mortent to make sure his comments are addressed

[mortent]

Looks good to me. Thanks for contributing!