try adding an sh_wrapper around heir-opt to populate env vars

[j2kun]

This should fix #885 (comment) but it needs way more testing

Tests run:

• bazel run with yosys optimizer: bazel run //tools:heir-opt -- --yosys-optimizer $PWD/tests/Transforms/yosys_optimizer/arith_ops.mlir
• bazel test a test target (for detecting runfiles dir) bazel test tests/Transforms/new_layout_propagation:add_one.mlir.test
• Running from bazel-bin: bazel-bin/tools/heir-opt --yosys-optimizer --canonicalize --cse --secret-forget-secrets $PWD/tests/Transforms/yosys_optimizer/arith_ops.mlir
• Frontend tests via bazel (bazel test frontend:e2e_test)

I still want to test:

• What happens when I install from the night release (in which case abc and the techmap files are in the same directory as the binary)
• Frontend tests when run from pip install -e .
• Frontend tests when run from pip install .
• Frontend tests when run from pip installing a pre-built wheel.

#vc4a