RFR: 7033677: potential cast error in MemberEnter [v2]

[Archie L. Cobbs]

> In an `import` statement, the thing imported is always a `JCFieldAccess` (it's not legal in Java to import a simple name).
> 
> Therefore the type of `JCFieldAccess.qualid`, which is currently `JCTree`, is unnecessarily wide and can be narrowed to `JCFieldAccess`.

Archie L. Cobbs has updated the pull request incrementally with one additional commit since the last revision:

  Fix Javadoc generator build broken by previous commit.

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Changes:
  - all: https://git.openjdk.org/jdk/pull/12606/files
  - new: https://git.openjdk.org/jdk/pull/12606/files/6fdc874d..391d7d18

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=12606&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=12606&range=00-01

  Stats: 9 lines in 1 file changed: 5 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/12606.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12606/head:pull/12606

PR: https://git.openjdk.org/jdk/pull/12606