[Java] Provide a utility to improve the performance of vector loading/unloading

[asfimport]

Vector loading/unloading transforms a set of vectors to and from a set of buffers with meta data. It is heavily used in flight/IPC.

In the loading/unloading operations, only the number of type buffers are really needed. However, the current code logic gets a copy of the type buffers, which is not necessary.

In this issue, we provide a utility to get the number of type buffers, given an arrow type. It improves the performance because it removes the following overhead:

1. creating type buffer objects unnecessarily.
2. creating a list and copying list contents (in TypeLayout#getBufferTypes) for vector unloading.

Reporter: Liya Fan / @liyafan82
Assignee: Liya Fan / @liyafan82

PRs and other links:

• GitHub Pull Request #5842

_{Note: This issue was originally created as ARROW-7177. Please see the migration documentation for further details.}