ARROW-5313: [Format] Comments on Field table are a bit confusing
ARROW-5313: [Format] Comments on Field table are a bit confusing

Move comments about specific attributes of `Field` into the definition to avoid confusion.

Author: Brian Hulette <bhulette@google.com>

Closes #4306 from TheNeuralBit/fbs-field-comment and squashes the following commits:

f500fd5e <Brian Hulette> triple-slash comments
a13b8ee2 <Brian Hulette> Clarify comment on Field table

icexelloss/arrow,kou/arrow,apache/arrow,majetideepak/arrow,xhochy/arrow,kou/arrow,wesm/arrow,majetideepak/arrow,majetideepak/arrow,majetideepak/arrow,cpcloud/arrow,icexelloss/arrow,renesugar/arrow,majetideepak/arrow,laurentgo/arrow,cpcloud/arrow,icexelloss/arrow,laurentgo/arrow,apache/arrow,icexelloss/arrow,renesugar/arrow,xhochy/arrow,apache/arrow,kou/arrow,wesm/arrow,apache/arrow,apache/arrow,majetideepak/arrow,renesugar/arrow,wesm/arrow,cpcloud/arrow,icexelloss/arrow,kou/arrow,xhochy/arrow,kou/arrow,xhochy/arrow,icexelloss/arrow,laurentgo/arrow,renesugar/arrow,laurentgo/arrow,cpcloud/arrow,wesm/arrow,wesm/arrow,kou/arrow,apache/arrow,wesm/arrow,xhochy/arrow,xhochy/arrow,xhochy/arrow,majetideepak/arrow,icexelloss/arrow,apache/arrow,renesugar/arrow,wesm/arrow,majetideepak/arrow,apache/arrow,wesm/arrow,wesm/arrow,laurentgo/arrow,renesugar/arrow,kou/arrow,cpcloud/arrow,apache/arrow,apache/arrow,laurentgo/arrow,xhochy/arrow,xhochy/arrow,icexelloss/arrow,renesugar/arrow,renesugar/arrow,icexelloss/arrow,majetideepak/arrow,xhochy/arrow,laurentgo/arrow,majetideepak/arrow,laurentgo/arrow,majetideepak/arrow,wesm/arrow,renesugar/arrow,renesugar/arrow,cpcloud/arrow,icexelloss/arrow,laurentgo/arrow,apache/arrow,kou/arrow,renesugar/arrow,apache/arrow,wesm/arrow,renesugar/arrow,majetideepak/arrow,kou/arrow,cpcloud/arrow,kou/arrow,cpcloud/arrow,majetideepak/arrow,apache/arrow,icexelloss/arrow,cpcloud/arrow,renesugar/arrow,kou/arrow,majetideepak/arrow,wesm/arrow,xhochy/arrow,icexelloss/arrow,renesugar/arrow,kou/arrow,laurentgo/arrow,laurentgo/arrow,majetideepak/arrow,laurentgo/arrow,cpcloud/arrow,xhochy/arrow,icexelloss/arrow,cpcloud/arrow,wesm/arrow,laurentgo/arrow,icexelloss/arrow,kou/arrow,xhochy/arrow,xhochy/arrow,cpcloud/arrow,apache/arrow,renesugar/arrow,cpcloud/arrow,wesm/arrow,kou/arrow,xhochy/arrow,laurentgo/arrow,laurentgo/arrow,cpcloud/arrow