Tests: Added an option to accept the actual token stream

[RunDevelopment]

Running npm run test:languages -- --accept will now insert the actual token stream of a test case to be the expect JSON. This will only be done if no expected JSON is specified.

Example

Test case:

var foo = 0;

Run npm run test:languages -- --accept.

Test case:

var foo = 0;

----------------------------------------------------

[
	["keyword", "var"],
	" foo ",
	["operator", "="],
	["number", "5"],
	["punctuation", ";"]
]

Motivation

This is super useful for creating many test cases at once.
When I create and change languages, I always have test drive open constantly check that every works. I then just copy the code from test drive I know work into test cases and copy their JSON from console output. This command makes my usual workflow a lot quicker.

It also makes it easier for first-time contributors to create test cases.

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This resolves #2401.