AK+Userland: Move AK/TestSuite.h into LibTest and rework Tests' CMake

As many macros as possible are moved to Macros.h, while the
macros to create a test case are moved to TestCase.h. TestCase is now
the only user-facing header for creating a test case. TestSuite and its
helpers have moved into a .cpp file. Instead of requiring a TEST_MAIN
macro to be instantiated into the test file, a TestMain.cpp file is
provided instead that will be linked against each test. This has the
side effect that, if we wanted to have test cases split across multiple
files, it's as simple as adding them all to the same executable.

The test main should be portable to kernel mode as well, so if
there's a set of tests that should be run in self-test mode in kernel
space, we can accomodate that.

A new serenity_test CMake function streamlines adding a new test with
arguments for the test source file, subdirectory under /usr/Tests to
install the test application and an optional list of libraries to link
against the test application. To accomodate future test where the
provided TestMain.cpp is not suitable (e.g. test-js), a CUSTOM_MAIN
parameter can be passed to the function to not link against the
boilerplate main function.

Userland/Libraries/LibSQL/Tests/TestSqlStatementParser.cpp

@@ -4,7 +4,7 @@
  * SPDX-License-Identifier: BSD-2-Clause
  */
 
-#include <AK/TestSuite.h>
+#include <LibTest/TestCase.h>
 
 #include <AK/Optional.h>
 #include <AK/Result.h>
@@ -735,5 +735,3 @@ TEST_CASE(common_table_expression)
     validate("WITH table (column1, column2) AS (SELECT * FROM table) DELETE FROM table;", { false, { { "table", { "column1", "column2" } } } });
     validate("WITH RECURSIVE table AS (SELECT * FROM table) DELETE FROM table;", { true, { { "table", {} } } });
 }
-
-TEST_MAIN(SqlStatementParser)