[antlr4] Change "boolean" -> "bool" because it causes problems during c++ code generation

[bshastry]

Description

I think this change is harmless for antlr tests but important for the upcoming antlr fuzzer (#9675 )

I filed an issue in the antlr repo (antlr/antlr4#2890) just to be sure.

[bshastry]

Looks like this may be an antlr4 issue and not related to our antlr grammar. Will wait for a response from the antlr4 team before resuming work on this.

[bshastry]

This is no longer an issue. Closing.