[WIP] [5/5] support C++20 Modules, construct build graph

[PikachuHyA]

I split the XXL PR https://github.com/bazelbuild/bazel/pull/19940 into several small patches. This is the fifth patch of Support C++20 Modules, I construct the build graph of compile with C++20 Modules.

Firstly, all files are scanned to generate .ddi files. All the .ddi files are then aggregated to create a .CXXModules.json file. Subsequently, based on the .CXXModules.json file and their respective .ddi files, .modmap files are generated. Finally, the compilation begins. The two-phase compilation is employed here.

              ┌────────┐                  ┌────────┐                  ┌────────┐
              │foo.cppm│                  │bar.cppm│                  │main.cc │
              └────┬───┘                  └────┬───┘                  └────┬───┘
c++20-deps-scanning│                           │                           │
                   │                           │                           │
              ┌────▼───┐                  ┌────▼───┐                  ┌────▼───┐
              │foo.ddi │                  │bar.ddi │                  │main.ddi│
              └────┬───┘                  └────┬───┘                  └────┬───┘
                   │                           │                           │
                   └───────────────────────────┼───────────────────────────┘
                                               │Cpp20ModulesInfoAction
                                      ┌────────▼───────────┐
                                      │demo.CXXModules.json│
                                      └────────────────────┘

                                              ┌────────────────────┐
                                              │demo.CXXModules.json│
                                              └─────┬──────────────┘
                                                    │
                                                    │
                                  ┌───────┐         │          ┌───────────┐
                               ┌─►│foo.ddi├─────────┤          │ bar.cppm  │
                               │  └───────┘         │          └─────┬─────┘
                               │                    │                │
                               │                    │                │
                               │                    │                │
                               │                    │                │
┌────────┐ c++20-deps-scanning │  ┌───────┐   ┌─────▼────┐      ┌────▼─────┐
│foo.cppm├─────────────────────┴─►│foo.d  │   │foo.modmap│      │ bar.pcm  │
└───┬────┘                        └──┬────┘   └────┬─────┘      └────┬─────┘
    │c++20-module-compile            │             │                 │
┌───▼───┐                            │             │                 │
│foo.pcm├────────────────────────────┴─────────────┼─────────────────┘
└───────┘                                          │c++20-module-codegen
                                              ┌────▼─────┐
                                              │ foo.o    │
                                              └──────────┘

Note: To make the code review convenient, I keep only one commit. Due to patch dependencies, it may build and test failed. I will update the patch after all the prerequisite patches have been merged. At that time, I will then troubleshoot the build and test failures.

[PikachuHyA]

as https://github.com/bazelbuild/bazel/pull/19940#discussion_r1608064853 mentioned, I will remove remove the reuse of the .d file.

[satyanandak]

@PikachuHyA Could you please take a look at the failing checks?

[PikachuHyA]

@PikachuHyA Could you please take a look at the failing checks?

This patch is dependent on the changes in https://github.com/bazelbuild/bazel/pull/22553. I will update this patch once that pull request has been merged.