Add libbej encoder wrapper for C++

Add unit tests and the test data files needed for unit tests.
Move APIs from bej_decoder_test.cpp to a common file, to share those
with bej_encoder_test.cpp

Tested:
Verified that encoding using the wrapper works well at runtime.
Verified that the unit tests pass.

Change-Id: I61b7c17690eb7e7fefd1973a22d4316c6214267e
Signed-off-by: Nikhil Namjoshi <nikhilnamjoshi@google.com>
diff --git a/test/meson.build b/test/meson.build
index a4ddfe1..c61ab8c 100644
--- a/test/meson.build
+++ b/test/meson.build
@@ -20,10 +20,14 @@
   'bej_common',
   'bej_dictionary',
   'bej_tree',
+  'bej_encoder'
 ]
+
+libbej_test_incs = include_directories('include')
 foreach t : gtests
   test(t, executable(t.underscorify(), t + '_test.cpp',
                      build_by_default: false,
                      implicit_include_directories: false,
+                     include_directories: libbej_test_incs,
                      dependencies: [libbej, gtest, gmock]))
 endforeach