Reuse buffers and reduce allocations in GSSInputStream

[vlsi]

Describe the issue

Currently, GSSInputStream makes a number of allocations for every read call.

In fact, we know backend never produces messages that exceed 16KiB, so we could use 16KiB buffer in case of GSS connection, and GSSInputStream could peek into VisibleBufferedInputStream's buffer.

The following allocations could be removed:

• pgjdbc/pgjdbc/src/main/java/org/postgresql/gss/GSSInputStream.java

  Line 39 in 450488c

  byte[] int4Buf = new byte[4];

• pgjdbc/pgjdbc/src/main/java/org/postgresql/gss/GSSInputStream.java

  Line 54 in 450488c

  byte[] encryptedBuffer = new byte[encryptedLength];