Adds support for lexing the argument encoding bitmap (presence bits).

[tgregg]

Description of changes:

This will be used basically as follows:

1. The application-level reader will advance the IonCursorBinary to the next token. The cursor conveys that it is positioned on a macro invocation.
2. The application-level reader retrieves the macro address from the cursor and retrieves the signature. If the signature requires an AEB, It initializes a PresenceBitmap (see Adds PresenceBitmap #895) from the signature.
3. If it has a PresenceBitmap, the reader calls the cursor's fillArgumentEncodingBitmap (added in this PR), providing the result of PresenceBitmap.byteSize(). This ensures the AEB byte(s) are buffered in a byte[] and allows the reader to retrieve the start and end indices.
4. The reader calls PresenceBitmap.readFrom(), providing the buffer and AEB start index accessible in the cursor.
5. The reader continues using the macro signature to manipulate the cursor accordingly.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.