Add the file a symbol is declared in to Reflection (#6613)

* Add the file a symbol is declared in to Reflection

If we move a code-generator to depend on Reflection,
it may need to know which file something was declared in
to properly name generated files.

* Doc comments in reflection, and more precise tests

* Add --project-root flag to flatc, normalize declaraion_file to this root

* fix --project-root stuff

* posixpath

* fix scripts

* format

* rename --project-root to --bfbs-filenames

Also, make it optional, rather than defaulting to `./`, if its not
specified, then don't serialize the filenames.

* bfbs generation

* fix some tests

* uncomment a thing

* add  to project root directory conditionally

* fix

* git clang format

* Added help description and removed != nullptr

* "

* Remove accidental change to docs

* Remove accidental change to docs

* Pool strings

Co-authored-by: Casper Neo <cneo@google.com>

CMakeLists.txt

@@ -443,6 +443,7 @@ function(compile_flatbuffers_schema_to_binary SRC_FBS)
     OUTPUT ${GEN_BINARY_SCHEMA}
     COMMAND "${FLATBUFFERS_FLATC_EXECUTABLE}"
             -b --schema --bfbs-comments --bfbs-builtins
+            --bfbs-filenames ${SRC_FBS_DIR}
             -I "${CMAKE_CURRENT_SOURCE_DIR}/tests/include_test"
             -o "${SRC_FBS_DIR}"
             "${CMAKE_CURRENT_SOURCE_DIR}/${SRC_FBS}"
@@ -468,6 +469,7 @@ function(compile_flatbuffers_schema_to_embedded_binary SRC_FBS OPT)
           --cpp-ptr-type flatbuffers::unique_ptr # Used to test with C++98 STLs
           ${OPT}
           --bfbs-comments --bfbs-builtins --bfbs-gen-embed
+          --bfbs-filenames ${SRC_FBS_DIR}
           -I "${CMAKE_CURRENT_SOURCE_DIR}/tests/include_test"
           -o "${SRC_FBS_DIR}"
           "${CMAKE_CURRENT_SOURCE_DIR}/${SRC_FBS}"