RFR: 8264779: Fix doclint warnings in java/nio

[Conor Cleary]

This fix addresses the following warnings which were generated by building JDK API documentation with the `-Xdoclint:all` option enabled:

./build/linux-x64/support/gensrc/java.base/java/nio/charset/IllegalCharsetNameException.java:47: warning: no comment
    private String charsetName;
                   ^
./open/src/java.base/share/classes/java/nio/charset/MalformedInputException.java:44: warning: no comment
    private int inputLength;
                ^
./open/src/java.base/share/classes/java/nio/charset/UnmappableCharacterException.java:44: warning: no comment
    private int inputLength;
                ^
./build/linux-x64/support/gensrc/java.base/java/nio/charset/UnsupportedCharsetException.java:47: warning: no comment
    private String charsetName;
                   ^
./open/src/java.base/share/classes/java/nio/file/DirectoryIteratorException.java:81: warning: no @param for s
    private void readObject(ObjectInputStream s)
                 ^
./open/src/java.base/share/classes/java/nio/file/DirectoryIteratorException.java:81: warning: no @throws for java.lang.ClassNotFoundException
    private void readObject(ObjectInputStream s)
                 ^
./open/src/java.base/share/classes/java/nio/file/FileSystemException.java:43: warning: no comment
    private final String file;
                         ^
./open/src/java.base/share/classes/java/nio/file/FileSystemException.java:44: warning: no comment
    private final String other;
                         ^
./open/src/java.base/share/classes/java/nio/file/InvalidPathException.java:43: warning: no comment
    private int index;
                ^
./open/src/java.base/share/classes/java/nio/file/InvalidPathException.java:42: warning: no comment
    private String input;
                   ^
./open/src/java.base/share/classes/java/nio/file/attribute/UserPrincipalNotFoundException.java:43: warning: no comment
    private final String name;
                         ^
Changes to [`genExceptions.sh`](https://github.com/openjdk/jdk/commit/b729d8ed7970737a8a2d4e8aa788df33789faea2) and the two [`exceptions`](https://github.com/openjdk/jdk/commit/b729d8ed7970737a8a2d4e8aa788df33789faea2) templates are to address the warnings concerned with `UnsupportedCharsetException.java` and `IllegalCharsetNameException.java` which are generated when `make jdk-image` is run. A CSR will be filed in due course with respect to these changes.

-------------

Commit messages:
 - 8264779: Doc fixes to generated exceptions
 - 8264779: Update copyrights and formatting
 - 8264779: Fix doclint warnings in java/nio

Changes: https://git.openjdk.java.net/jdk/pull/3376/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=3376&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8264779
  Stats: 48 lines in 9 files changed: 38 ins; 0 del; 10 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3376.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3376/head:pull/3376

PR: https://git.openjdk.java.net/jdk/pull/3376