Provide better messages for code involving infix operators

[rossellhayes]

• When only one of solution or submitted is an infix, provide the whole context,
  • e.g. "I expected you to call mean() where you called (x + y)/2."
• When both solution and submitted are infixes, provide jus the operator,
  • e.g. "I expected you to call + where you called *."

Closes #84.

TODO

• Consider Improve identification of infix operators #225
  • Closed by Add more operators to list of infixes #327
• Consider code_feedback() gives misleading message when an infix operator is replaced with a comma #272
• Fix handling of chained infixes

user <- "sqrt(1 + 2)"
solution <- "sqrt(1 + 2 + 3)"
code_feedback(user, solution)
#> In `1 + 2`, I expected `1 + 2` where you wrote `1`.

• Don't reveal the contents of functions that are infix arguments

user <- "b(1)"
solution <- "b(1) + 2"
code_feedback(user, solution)
#> I expected you to call `b(1) + 2` where you called `b()`.

• Investigate how we give feedback on the base pipe (|>)
• Improve handling of repeated operators (e.g. !!, !!! and {{ }})

^{Created on 2023-02-16 with reprex v2.0.2}

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