includeUnusedVariables support for BatchHTTPLink

[ShawnToubeau]

Intended outcome:
Hello there! I was noticing a bug in my team's application when we recently made the change from using HTTPLink to BatchHTTPLink and some of our queries started to fail because of unused variables.
We've tried setting includeUnusedVariables in our BatchHTTPLink constructor but that had no effect. When looking through the batchHttpLink.ts code I noticed that the variable requestOptions didn't inherit includeUnusedVariables from fetchParams, which is eventually passed to linkConfig.options.

Actual outcome:
BatchHTTPLink should strip unused variables by default just like HTTPLink and have the option of disabling it. See second bullet point here in the 3.3.0 change-log for details on behavior.

How to reproduce the issue:
With any Apollo Client implementation, swap out HTTPLink with BatchHTTPLink. Then, with any query/mutation, pass it extra variables and there should be an error thrown when unused variables are provided.

Versions
System:
OS: macOS 11.5.2
Binaries:
Node: 16.6.2 - /usr/local/bin/node
Yarn: 1.22.5 - ~/.yarn/bin/yarn
npm: 7.20.3 - /usr/local/bin/npm
Browsers:
Chrome: 93.0.4577.82
Firefox: 92.0
Safari: 14.1.2
npmPackages:
@apollo/client: 3.3.19 => 3.4.13
apollo-link-sentry: 3.0.2 => 3.0.2

[jerelmiller]

Hello 👋

This has been fixed with #10754 and will go out with the next 3.8.0-alpha.x release. Thanks for reporting this!

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