go_path and generated sources results in conflicts when combining architectures

I have the use case where I need to ship parts of the source code, so that this part can be built externally.

`go_path` works generally pretty well for this as it allows to collect all dependencies and provides a defined path to build from there.

But to make sure that the shipped code is universal, I have to include the sources for different platforms/architectures (e.g. `foo_darwin.go`, `foo_windows.go`, etc).

This is currently solved by defining several targets as entry points (one for each platform/arch pair we support) and having them as dependencies for `go_path`.

Example

```python
PLATFORMS = [
("windows", "amd64"),
("windows", "386"),
("linux", "amd64"),
("linux", "386"),
("linux", "arm"),
("linux", "arm64"),
("darwin", "amd64"),
("darwin", "arm64"),
]
[
go_binary(
name = "binary_%s_%s" % (goos, goarch),
embed = [":binary_lib"],
goarch = goarch,
goos = goos,
visibility = ["//visibility:public"],
)
for goos, goarch in PLATFORMS
]

go_path(
name = "my_gopath",
deps = [
"//:binary_%s_%s" % (goos, goarch)
for goos, goarch in PLATFORMS
],
)
```

This generally works well, but falls apart when generated source files come into play:

```
Traceback (most recent call last):
File "/external/rules_go+/go/private/tools/path.bzl", line 76, column 32, in _go_path_impl
_add_manifest_entry(manifest_entries, manifest_entry_map, inputs, f, dst)
File "/external/rules_go+/go/private/tools/path.bzl", line 277, column 17, in _add_manifest_entry
fail("{}: references multiple files ({} and {})".format(dst, entry_map[dst], src.path))
Error in fail: /file.gen.go: references multiple files (bazel-out/k8-fastbuild-ST-b9eeda35ed41/bin//file.gen.go and bazel-out/k8-fastbuild-ST-1cb734d4f317/bin//file.gen.go)
```

(where `file.gen.go` is created by a `genrule`, only depending on other files, no tools)

Is there a better way of doing this, or can this be otherwise fixed somehow?

Versions
- rules_go: 0.59.0
- gazelle: 0.47.0

Start with go/private/tools/path.bzl, especially _go_path_impl and _add_manifest_entry, and reproduce the go_path setup with architecture-specific targets and generated file.gen.go sources. Trace why identical destination paths from different bazel-out configurations collide. Done means combining the listed platforms succeeds without conflicting manifest entries while preserving the generated sources.

Written by the indexing model from the issue text.