[url] move url to library (#5233)

This commit moves the URL parser to src/lib.

Also includes the following changes:
- Split URL on initialization.
- Make a GetValue() const method.
- Check aLastValue.
- Add some negative tests.

CMakeLists.txt

@@ -40,7 +40,11 @@ set(OT_EXTERNAL_MBEDTLS "" CACHE STRING "Specify external mbedtls library")
 
 add_library(ot-config INTERFACE)
 
-target_include_directories(ot-config INTERFACE ${PROJECT_SOURCE_DIR}/src/core)
+target_include_directories(ot-config INTERFACE
+    ${PROJECT_SOURCE_DIR}/include
+    ${PROJECT_SOURCE_DIR}/src
+    ${PROJECT_SOURCE_DIR}/src/core
+)
 
 include(TestBigEndian)
 TEST_BIG_ENDIAN(OT_BIG_ENDIAN)