fix: check the existence of Proxy

[ambar]

This is useful when importing the package in legacy browsers (especially umd).

Related: #1178
Closes: #1178

[codesandbox-ci]

This pull request is automatically built and testable in CodeSandbox.

To see build info of the built libraries, click here or the icon next to each commit SHA.

Latest deployment of this branch, based on commit c4aa7f8:

Sandbox	Source
Framer Motion: Simple animation	Configuration
App Store UI using React and Framer Motion	Configuration
Framer Motion: Reorder animation	Configuration
Framer Motion: growing item positionTransition issue	Configuration
Framer Motion: Image lightbox	Configuration

[mattgperry]

Nice approach, this would still break in older browsers but would at least allow people who need this to do

const Component = motion("div")

[ambar]

Also handy for calling m().

In current version we cannot construct m() because createDomMotionConfig is not exported.