This fixes a few build issues from iguana that have been catched by CI:
- Move the directory to src/ where it belongs, fixing the include paths and sanitizer linkage
- Fix the description because it's not bitcoin-tx
- Exclude from the default install so we don't ship the binary that currently is an empty shell
- Build the iguana target first before running the tests on CI. This is not a behavior change because the dependencies are set properly, but it will help stop the build early if it fails so it makes parsing CI easier