Consider using Bazel 'Args'

If possible it's often better to use Bazel's Args construct to generate flags for binaries. It has automatic conversions for files and the like.

https://bazel.build/rules/lib/builtins/Args

This originated from a comment by @QuantamHD, considering args processing as shown below from https://github.com/google/xls/blob/main/xls/build_rules/xls_codegen_rules.bzl:

```
final_args += " --output_block_ir_path={}".format(block_ir_file.path)
```