RFR: JDK-8267219: Javadoc method summary breaks when {@inheritDoc} from an empty parent

[liach]

This change fixes when a method body has only inline tags that produce no output, the method summary will get eaten.

This change allows `{@inheritDoc}` from empty parents to go through the code path used by `-nocomment` and properly generate tables.

All `jtreg:test/langtools/jdk/javadoc/doclet` tests pass.

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Commit messages:
 - JDK-8267219 : Javadoc method summary breaks when {@inheritDoc} from an empty parent

Changes: https://git.openjdk.java.net/jdk/pull/4066/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=4066&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8267219
  Stats: 124 lines in 4 files changed: 118 ins; 0 del; 6 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4066.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4066/head:pull/4066

PR: https://git.openjdk.java.net/jdk/pull/4066