install: Add EXCLUDE_FROM_ALL option (#14921)

Let us take an example of a project that has some tests in a component
that need to be installed into a dedicated test package.  The user
expectation is that the result could be achieved by typing the
following:

    make
    make tests
    make install
    DESTDIR=/testpkgs make install-tests

However this results in test components in the default installation as
well as the testpkg.

Add an EXCLUDE_FROM_ALL option to the install() command to tell it that
the installation rule should not be included unless its component is
explicitly specified for installation.

Source/cmInstallFilesGenerator.cxx

@@ -24,9 +24,11 @@ cmInstallFilesGenerator
                           std::vector<std::string> const& configurations,
                           const char* component,
                           MessageLevel message,
+                          bool exclude_from_all,
                           const char* rename,
                           bool optional):
-  cmInstallGenerator(dest, configurations, component, message),
+  cmInstallGenerator(dest, configurations, component, message,
+                     exclude_from_all),
   LocalGenerator(0),
   Files(files),
   FilePermissions(file_permissions),