RFR: 8320781: Fix whitespace in j.l.Double and j.u.z.ZipInputStream @snippets

[Eirik Bjorsnos]

Please review this trivial, formatting and documentation-only change which adds missing whitespace around a few `if` statements, `while` statements and assigments in `@snippet` code in `j.l.Double` and `j.u.z.ZipInputStream`.

While there are many similar issues in the OpenJDK code base, these were the only instances found in `@snippet` code in the API of `java.base`, so it could be worthwhile fixing. 

While updating the snippet in `ZipInputStream`, I took the liberty to also add `lang = "java"` since this seems more commonly included around the code base.

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Commit messages:
 - Correct whitespace around if, while and assignments in @snippet code in java.base

Changes: https://git.openjdk.org/jdk/pull/16827/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=16827&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8320781
  Stats: 5 lines in 2 files changed: 0 ins; 0 del; 5 mod
  Patch: https://git.openjdk.org/jdk/pull/16827.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16827/head:pull/16827

PR: https://git.openjdk.org/jdk/pull/16827