JDK 16 RFR of JDK-8248428: Cleanup pass on javax.lang.model docs​

[Joe Darcy]

Hello,

Please review the changes for

     JDK-8248428: Cleanup pass on javax.lang.model docs​
     http://cr.openjdk.java.net/~darcy/8248428.0/

a small pass to polish the docs, many new @jls tags added in the type 
package.

Thanks,

-Joe