Hygiene issue with indicator constraints

[blegat]

model = Model()
@variable(model, b, Bin)
@variable(model, x)
@constraint(model, b => {x in MOI.EqualTo(1.0)})

gives

ERROR: LoadError: UndefVarError: `##3910` not defined
Stacktrace:
 [1] macro expansion
   @ ~/.julia/packages/JuMP/W1IDA/src/macros/@constraint.jl:171 [inlined]
 [2] macro expansion
   @ ~/.julia/packages/JuMP/W1IDA/src/macros.jl:393 [inlined]

The hygiene seems ok if you do x == 1 but not with the in syntax

[odow]

Hmm. Yeah. I don't think we considered this, but we should throw a nicer error message.

[odow]

Simple fix: #3813