Deprecate the `helper` wrapper function coming from `@ember/component/helper`

[bertdeblock]

Motivation:

• We can use plain functions as helpers since ember-source@4.5.0
• We've removed it from the helper blueprint since ember-source@6.3.0

Are there any reasons to keep it around that I might be missing?

[NullVoxPopuli]

there is one reason to maybe keep it around:

• helper() is the only utility we have right now for allowing lazily consumed arguments to a function-ish helper

that is, regular functions' trackedness is all consumed upon evaluation of the function -- where as with helper(), you only track what is used in the helper().

is that enough of a reason to keep helper() around?
idk

Does it cost us much to keep around? not really.

Could there be a perf difference between helper() and plain functions? maybe -- I'd love to see some analysis on this