test: add test for multiple inlined modules

[fi3ework]

What kind of change does this PR introduce?

Currently, there's no test case covering the following condition, if we comment this condition, no test will fail.

webpack/lib/javascript/JavascriptModulesPlugin.js

Lines 849 to 850 in c586c7b

	: inlinedModules.size > 1
	? // TODO check globals and top-level declarations of other entries and chunk modules

Did you add tests for your changes?

Adding a multiple inline modules case to cover the condition. Multiple entry file have declared same identifiers, so does non-inline modules to make sure it won't break in a more complex scenario.

Does this PR introduce a breaking change?

No.

What needs to be documented once your changes are merged?

No.

[webpack-bot]

For maintainers only:

• This needs to be documented (issue in webpack/webpack.js.org will be filed when merged)
• This needs to be backported to webpack 4 (issue will be created when merged)