RFR: 8287333: Clean up ParamTaglet and ThrowsTaglet

[Pavel Rappo]

A cleanup to facilitate fixing bugs like JDK-6509045: `{@inheritDoc}` only copies one instance of the specified exception.

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Commit messages:
 - Update top-level doc comment
 - Trivially re-order assignments
 - Reformat for clarity
 - Remove dead condition
 - Remove emptiness check
 - Remove comments
 - Use consistent order
 - Rename and clarify
 - Improve `inherit`
 - Rearrange methods
 - ... and 16 more: https://git.openjdk.java.net/jdk/compare/e990fec1...03ec6e6f

Changes: https://git.openjdk.java.net/jdk/pull/8886/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8886&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8287333
  Stats: 382 lines in 3 files changed: 111 ins; 158 del; 113 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8886.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8886/head:pull/8886

PR: https://git.openjdk.java.net/jdk/pull/8886