Merge [*RaisesException] extended attributes

Consolidates 4 extended attributes into 1:
[RaisesException] => [RaisesException]
[GetterRaisesException] => [RaisesException=Getter]
[SetterRaisesException] => [RaisesException=Setter]
[ConstructorRaisesException] => [RaisesException=Constructor]

No changes to generated code.

Docs updated:
https://sites.google.com/a/chromium.org/dev/blink/webidl/blink-idl-extended-attributes#TOC-RaisesException-m-a-i-

Review URL: https://codereview.chromium.org/68423002

git-svn-id: svn://svn.chromium.org/blink/trunk@161794 bbb929c8-8fbe-4397-9dbb-9b2b20218538