Fix host tool selection in armhf cross builds

[tzhengus]

What changed

Fix four host/target mismatches in the armhf cross-build path, as four focused commits:

1. select esbuild:native because the build host executes esbuild;
2. select rustfmt:native because source generation executes rustfmt;
3. make Perfetto's run_binary.py prepend HOST_EXEC_WRAPPER when set;
4. make dump_app_syms.py wrap the target dump_syms binary while leaving the later system strip command native.

Tracks #62.

Why

With dpkg-buildpackage -B --host-arch armhf -Pcross on an x86-64 Trixie builder, unqualified build-tool dependencies resolve to armhf and cannot be executed natively. Chromium 150 also has runners that execute generated armhf helpers without the cross-exe-wrapper path already used elsewhere in the Debian packaging.

These changes affect build dependencies and build-time process launching only; they do not change Chromium runtime behavior.

Validation

• cross-profile dependency resolution was checked for esbuild and rustfmt;
• both Python patches pass syntax checks;
• command-level smoke tests confirm HOST_EXEC_WRAPPER is applied to the intended target binary;
• the real armhf package build has progressed past the original esbuild, rustfmt, and Perfetto failures;
• the complete package build, including the final Breakpad symbol action and .deb output, is still running.

This PR is intentionally a draft. I will add the final armhf package result before marking it ready. The four commits can be split into separate PRs if that is easier to review.