Convert Existence Checks to Embroider Macros

[richgt]

Description

Create new Babel Transform to convert module existence checks to Embroider Macros.

for: #8103

Type of PR

What kind of change is this?

• [X] refactor

Notes for the release

Does this PR need to be described in the Ember release blog post? Please briefly describe what should be shared.

Probably not :-D