test: add invalid-lone-import test

[JLHwung]

Q	A
License	MIT

This PR removes an unreachable unexpected check, so it is not covered in any unit test:
https://codecov.io/gh/babel/babel/src/b91720c1ccbfc066cbc6af7e3db6114acefac17a/packages/babel-parser/src/parser/expression.js#L929

If the next token is neither tt.dot nor tt.parenL, it will be parsed in parseStatementContent

babel/packages/babel-parser/src/parser/statement.js

Lines 222 to 229 in daaa206

	case tt._import: {
	const nextTokenCharCode = this.lookaheadCharCode();
	if (
	nextTokenCharCode === charCodes.leftParenthesis ||
	nextTokenCharCode === charCodes.dot
	) {
	break;
	}

Add a new lone-import test for coverage.

[nicolo-ribaudo]

That check should be tested, not removed 😛

https://babeljs.io/repl/build/14450#?browsers=&build=&builtIns=usage&spec=false&loose=false&code_lz=BQSwtgDg9gTgLgSgNxA&debug=false&forceAllTransforms=false&shippedProposals=false&circleciRepo=&evaluate=false&fileSize=false&timeTravel=true&sourceType=script&lineWrap=false&presets=env&prettier=false&targets=&version=7.7.7%2Bpr.10950&externalPlugins=

[nicolo-ribaudo]

While looking at this error, I realized that we can use this.raise to provide a better error message: "import" can only be used as part of dynamic import() or import.meta.
Also, since the most common error would probably be thinking of import() as a function call and thus of import as a norma identifier that you can pass around, recovering from this error by using it as a norma expression makes sense.