CMake: Build LibRegex tests in Tests/LibRegex not Meta/Lagom

As LibRegex was not specified in TEST_DIRECTORIES, the existing
Tests/LibRegex subdirectory was not actually included during
configuration. Also the RegexLibC test has not been needed
since migration away from Serenitys LibC was done, so
that test has been fully removed. I also renamed the
Regex.cpp test to TestRegex.cpp to match the naming
convention of most test targets.

Meta/Lagom/CMakeLists.txt

@@ -483,6 +483,7 @@ if (BUILD_TESTING)
         LibCore
         LibDNS
         LibGC
+        LibRegex
         LibTest
         LibTextCodec
         LibThreading
@@ -511,10 +512,6 @@ if (BUILD_TESTING)
     # LibTLS needs a special working directory to find cacert.pem
     lagom_test(../../Tests/LibTLS/TestTLSHandshake.cpp LibTLS LIBS LibTLS LibCrypto)
     lagom_test(../../Tests/LibTLS/TestTLSCertificateParser.cpp LibTLS LIBS LibTLS LibCrypto)
-    
-    # RegexLibC test POSIX <regex.h> and contains many Serenity extensions
-    # It is therefore not reasonable to run it on Lagom, and we only run the Regex test
-    lagom_test(../../Tests/LibRegex/Regex.cpp LIBS LibRegex WORKING_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}/../../Tests/LibRegex)
 
     # JavaScriptTestRunner + LibTest tests
     # test-js

Tests/LibRegex/CMakeLists.txt

@@ -1,6 +1,5 @@
 set(TEST_SOURCES
-    Regex.cpp
-    RegexLibC.cpp
+    TestRegex.cpp
 )
 
 foreach(source IN LISTS TEST_SOURCES)