Make a copy of Matrix in CursorAnchorInfoBuilder

This CL fixes a bug that CursorAnchorInfoBuilder does't make a
copy if the Matrix specified with #setMatrix.

Without this fix, IMM#updateCursorAnchorInfo could fail to detect
duplicated events when the same instances of
CursorAnchorInfoBuilder and Matrix are reused to optimize
performance.

Change-Id: I50c50a12a06d3cda4dec445b171b61ceb78da21a