* Rename `ILBuilder` to `FunctionBuilderContext` and update corresponding
code
* Refactor usages of ILBuilder to become FunctionBuilderContext,
update variable names to reflect this change
* Reformat to ensure that lines stay under 100 char limit
* Apply corrections from `rustfmt` to pass tests
* Rename variables to be more consistent with refactor of ILBuilder
9128290fb4