Fix Compiled props being incorrectly forwarded when default values used

Fixes #1629

https://github.com/atlassian-labs/compiled/blob/9860df3850ac5023ffa93201f5648fd7c81807c5/packages/babel-plugin/src/utils/build-styled-component.ts#L80 expects a MemberExpression in order to detect what props shouldn't be forwarded to React. All other props are forwarded to React. (see this PR for more context: https://github.com/atlassian-labs/compiled/pull/1273)

However, when we handle default values in situations like these...

import { styled } from '@compiled/react';
const styled.div({
    margin: ({ marginTop = 12 }) => marginTop,
});

@compiled/babel-plugin used the t.identifier function to generate the __cmplp.marginTop expression:

styled.div<{
  marginTop?: string;
}>({
  marginTop: __cmplp => __cmplp.marginTop ?? '24px'
})

The above appears correct, because the build output is identical and Babel doesn't stop us from passing invalid expressions to the t.identifier function... however, the use of t.identifier and t.memberExpression meant that it would never get detected as a MemberExpression, and thus the prop would never not be forwarded to React :(

This PR fixes this by replacing t.identifier with t.memberExpression.

atlassian-labs / compiled

Fix Compiled props being incorrectly forwarded when default values used #1630

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