Bazel: general improvements. (#1043)

* Bazel: general improvements.

Improve the Bazel build. Attempt to fix previous errors recorded while
trying to publish ftxui in the Bazel Central Registry:
- https://github.com/bazelbuild/bazel-central-registry/pull/4485
- https://buildkite.com/bazel/bcr-presubmit/builds/13601#01968b61-f5b2-4d16-94d0-c87a03a1a23b

Test against "recent" platforms
-------------------------------

Previously, I got the error:
```
gcc: error: unrecognized command line option '-std-c++20'; did you mean '-std-c++2a'?
```
This was due to using old distribution like ubuntu 2004. Test against
newer platforms only to avoid GCC version<-9.x.y

Downgrade gtest version.
------------------------

I suspect this caused the Bazel Central Registry error:
```
file:///workdir/modules/googletest/1.15.2/MODULE.bazel:68:20: name 'use_repo_rule' is not defined
```
Specifying using bazelmod fixes the issue. Thanks @robinlinden

Tag gtest as dev_dependency
---------------------------

Presumably, this should avoid dependants to fetch it?

Enable --features-layering_check
--------------------------------

Aka clang `-Wprivate-header`. Fix the encountered errors.

Use clang in the CI
-------------------

The CI was defining clang/gcc in the matrix, but was not using it. Fix
the bug.

.github/workflows/build.yaml

@@ -14,25 +14,30 @@ on:
 jobs:
 
   test_bazel:
-    name: "Bazel, ${{ matrix.compiler }}, ${{ matrix.os }}"
+    name: "Bazel, ${{ matrix.cxx }}, ${{ matrix.os }}"
     strategy:
       fail-fast: false
       matrix:
         include:
           - os: ubuntu-latest
-            compiler: gcc
+            cxx: g++
+            cc: gcc
 
           - os: ubuntu-latest
-            compiler: llvm
+            cxx: clang++
+            cc: clang
 
           - os: macos-latest
-            compiler: llvm
+            cxx: g++
+            cc: gcc
 
           - os: macos-latest
-            compiler: gcc
+            cxx: clang++
+            cc: clang
 
           - os: windows-latest
-            compiler: cl
+            cxx: cl
+            cc: cl
 
     runs-on: ${{ matrix.os }}
     steps:
@@ -40,10 +45,16 @@ jobs:
         uses: actions/checkout@v3
 
       - name: "Build with Bazel"
+        env:
+          CC: ${{ matrix.cc }}
+          CXX: ${{ matrix.cxx }}
         run: bazel build ...
 
       - name: "Tests with Bazel"
-        run: bazel run tests
+        env:
+          CC: ${{ matrix.cc }}
+          CXX: ${{ matrix.cxx }}
+        run: bazel test --test_output=all ...
 
   test_cmake:
     name: "CMake, ${{ matrix.compiler }}, ${{ matrix.os }}"