Include identifying information (e.g. crate names) in --dump-* filenames.

[eddyb]

Before

$ RUSTGPU_CODEGEN_ARGS="--dump-pre-link=$PWD/dumps/pre-link \
                        --dump-post-merge=$PWD/dumps/post-merge \
                        --dump-post-split=$PWD/dumps/post-split \
                        --dump-post-link=$PWD/dumps/post-link \
                        --spirt --dump-spirt-passes=$PWD/dumps/spirt-passes" \
  cargo run -p example-runner-wgpu
⋮
   Compiling sky-shader v0.0.0 (⋯/examples/shaders/sky-shader)
⋮
$ tree dumps
dumps
├── pre-link
│   ├── mod_0.spv
│   ├── mod_1.spv
│   ⋮
│   ├── mod_383.spv
│   └── mod_384.spv
├── post-merge
├── spirt-passes
├── spirt-passes.html
├── post-split
│   └── mod_0.spv
└── post-link
    └── module

After

$ RUSTGPU_CODEGEN_ARGS="--dump-pre-link=$PWD/dumps/pre-link \
                        --dump-post-merge=$PWD/dumps/post-merge \
                        --dump-post-split=$PWD/dumps/post-split \
                        --dump-post-link=$PWD/dumps/post-link \
                        --spirt --dump-spirt-passes=$PWD/dumps/spirt-passes" \
  cargo run -p example-runner-wgpu
⋮
   Compiling sky-shader v0.0.0 (⋯/examples/shaders/sky-shader)
⋮
$ tree dumps
dumps
├── pre-link
│   ├── bitflags-8e60e58c2f5bbf61.bitflags.066dfbae-cgu.0.rcgu.spv
│   ├── bytemuck-b3e7e930e0f4de73.bytemuck.2753b143-cgu.0.rcgu.spv
│   ⋮
│   ├── shared-6aad9625adbcf25a.3o3jyhwfr4jh2s1n.rcgu.spv
│   ├── sky_shader.19029ydyojn6ny4z.rcgu.spv
│   ├── spirv_std-ebcff9dfacf15505.3zchoimcc4ql6s81.rcgu.spv
│   ⋮
│   ├── spirv_std-ebcff9dfacf15505.gw065rptpzqehcz.rcgu.spv
│   └── spirv_std_types-2758271e2b6a2802.2k6ghdgur5korza1.rcgu.spv
├── post-merge
│   └── sky_shader.spv
├── spirt-passes
│   ├── sky_shader.spirt
│   └── sky_shader.spirt.html
├── post-split
│   └── sky_shader.spv
└── post-link
    └── sky_shader.spv

$ RUSTGPU_CODEGEN_ARGS="--dump-pre-link=$PWD/dumps/pre-link \
                        --dump-post-merge=$PWD/dumps/post-merge \
                        --dump-post-split=$PWD/dumps/post-split \
                        --dump-post-link=$PWD/dumps/post-link \
                        --spirt --dump-spirt-passes=$PWD/dumps/spirt-passes" \
  cargo run -p multibuilder
⋮
   Compiling sky-shader v0.0.0 (⋯/examples/shaders/sky-shader)
⋮
$ tree dumps
dumps
├── pre-link
│   ⋮
├── post-merge
│   └── sky_shader.spv
├── spirt-passes
│   ├── sky_shader.spirt
│   └── sky_shader.spirt.html
├── post-split
│   ├── sky_shader.main_fs.spv
│   └── sky_shader.main_vs.spv
└── post-link
    ├── sky_shader.main_fs.spv
    └── sky_shader.main_vs.spv

(dumps/pre-link omitted as it's identical between the single-module and multi-module modes)

---

This idea first came up in the context of --dump-spirt-passes (from #940) - which we want to be able to set once for shader builders that build several shaders (or potentially even the entire test suite, heh), but it turns out that pretty much all existing --dump-* also have the problem of not being able to tell anything apart.

Hopefully the above before/after comparison speaks for itself!