Add keyIsInjected helper

[The-Compiler]

So that the bits don't have to be masked and checked manually, like with the other helpers. This avoids mistakes like in #1076 (will add a review comment with details shortly).

I was unable to run the tests locally due to #1081, so I'll rely on the CI instead and hope I didn't mess something up. Refactorings were done via:

git ls-files | xargs sed -i 's/(event\.state \& INJECTED) != 0/keyIsInjected(event.state)/g'
git ls-files | xargs sed -i 's/(event\.state \& INJECTED) == 0/!keyIsInjected(event.state)/g'  
git ls-files | xargs sed -i 's/(event\.state \& INJECTED)/(keyIsInjected(event.state))/g'