[lang] support multiline arguments to annotations

[cppforlife]

Describe the problem/challenge you have I want to be able to annotate a node using an expression formatted over multiple lines, but ytt currently only accepts a single line per annotation.

Describe the solution you'd like For example,

#@schema/desc """
#@ something something
#@ """
a: 123

#@overlay/match by=overlay.subset({
#@  "kind": "Foo",
#@  "metadata": {"blah": "blah"},
#@ })
b: 123

Anything else you would like to add:

---

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[pivotaljohn]

Requested: https://kubernetes.slack.com/archives/CH8KCCKA5/p1650629876052489

[cmoulliard]

We should also to have the possibility to pass the function to the next line Now

--- #@ generate_certificate(name,namespace,cert_duration,cert_renew_before,cert_secret_name,common_name,dns_names,cert_subject, cert_keystore, issuer_name)

Expected

--- 
#@ generate_certificate(name,namespace,cert_duration,cert_renew_before,cert_secret_name,common_name,dns_names,cert_subject, cert_keystore, issuer_name)

and pass the args on multilines Now

--- #@ generate_certificate(name,namespace,cert_duration,cert_renew_before,cert_secret_name,common_name,dns_names)

Expected

--- 
#@ generate_certificate(name,namespace, 
                        cert_duration,
                        cert_renew_before,
                        cert_secret_name,
                        common_name,
                        dns_names)

[pivotaljohn]

We should also to have the possibility to pass the function to the next line

I see how the format you're looking for is more intuitive. 👍🏻

However, it's one thing to recognize an annotation is spilling over onto subsequent lines. It's a whole 'nother thing to start to attach annotations to a node that is above the annotation.

Little known fact: the #@ is a short-hand for two annotations. When #@ appears to the right of a node, it's (internally) identified as a #@template/value annotation. When there is no node to the left of the annotation it's a #@template/code.

• @template/value annotations compile into code that sets the value on the decorated node.
• @template/code contributes raw Starlark code to the template.

So, we'd start introducing corner-cases into this crucial "algorithm" that identifies to which node an annotation is attached and what kind of @template/... annotation is implied.

Not saying it's not possible; noting the internal complexity that would result (which increases the risk of bugs).