RFR: 8357178: Simplify Class::componentType [v2]

[Chen Liang]

> `isArray` and null return is now redundant when `componentType` is changed to an explicit field.

Chen Liang has updated the pull request incrementally with one additional commit since the last revision:

  For parity with MT.descriptorString

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Changes:
  - all: https://git.openjdk.org/jdk/pull/25280/files
  - new: https://git.openjdk.org/jdk/pull/25280/files/272ee25d..f8f0bf65

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=25280&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=25280&range=00-01

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/25280.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25280/head:pull/25280

PR: https://git.openjdk.org/jdk/pull/25280