RFR: 8304367: jlink --include-locales=* attempts to parse non .class resource files with classfile reader [v2]

[Naoto Sato]

> This is a blocker for [JDK-8294972](https://bugs.openjdk.org/browse/JDK-8294972). The fix is to weed out non-class files for calling `ClassReader` by checking the file extension. Regression tests are not provided as it is not possible to detect the fix from the artifact jimage, but manually confirmed it would effectively weed out `LineBreakIteratorData_th`, `WordBreakIteratorData_th`, and `thai_dict` files by running `IncludeLocalesPluginTest.java`.

Naoto Sato has updated the pull request incrementally with one additional commit since the last revision:

  eliminate redundant call

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/13067/files
  - new: https://git.openjdk.org/jdk/pull/13067/files/d7ad21cb..b837e4d8

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=13067&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=13067&range=00-01

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/13067.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/13067/head:pull/13067

PR: https://git.openjdk.org/jdk/pull/13067