pw_ide: Manage C++ compilation DBs

GN and other build systems can generate clangd compilation databases
(compile_commands.json) for Pigweed projects, but because these projects
usually have multiple targets/toolchains, as well as targets that aren't
actually clang/GCC compile commands (e.g. Python wrappers for code
analysis), those files won't work reliably with clangd without
processing. Processing yields several consistent and valid compilation
databases, one for each valid target. Additional tools allow selection
of which compilation database clangd should use via a stable symlink in
the working directory.

Change-Id: Ib13155feca7e8a056b4b32a0d54ce0a179f1cace
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/110253
Reviewed-by: Anthony DiGirolamo <tonymd@google.com>
Commit-Queue: Chad Norvell <chadnorvell@google.com>

pw_ide/docs.rst

@@ -15,3 +15,10 @@ these options can be configured:
   (by default this is `.pw_ide` in the project root). This directory shouldn't
   be committed to your repository or be a directory that is routinely deleted or
   manipulated by other processes.
+
+* ``targets``: A list of build targets to use for code analysis, which is likely
+  to be a subset of the project's total targets. The target name needs to match
+  the name of the directory that holds the build system artifacts for the
+  target. For example, GN outputs build artifacts for the
+  ``pw_strict_host_clang_debug`` target in a directory with that name in the
+  ``out`` directory. So that becomes the canonical name for that target.

pw_ide/py/BUILD.gn

@@ -25,9 +25,15 @@ pw_python_package("py") {
   sources = [
     "pw_ide/__init__.py",
     "pw_ide/__main__.py",
+    "pw_ide/cpp.py",
+    "pw_ide/exceptions.py",
     "pw_ide/settings.py",
+    "pw_ide/symlinks.py",
+  ]
+  tests = [
+    "cpp_test.py",
+    "test_cases.py",
   ]
-  tests = []
   python_deps = [ "$dir_pw_console/py" ]
   pylintrc = "$dir_pigweed/.pylintrc"
 }