RFR: 8371795: Improve documentation of Class.isInstance [v4]

[Chen Liang]

> The 3 methods to determine conversions and subtyping on `java.lang.Class`, which are `isInstance`, `cast`, and `isAssignableFrom`, have their documentation from the earliest days of the Java Platform. During the language evolution, a lot of terms have become inaccurate, such as "assignment-compatible", which does not apply for primitive types, and the out-of-date instanceof analogy with the upcoming patterns, in `isInstance`; `isAssignableFrom` is not very clear about arrays; `cast` would also benefit from more detailed explanations.
> 
> In my facelift, I moved the subtyping description to `isAssignableFrom`, and left the conversion stuff in `isInstance` and `cast`.  I intentionally avoided linking to too many JLS chapters to reduce confusions. I believe in this shape, we have a good amount of easily comprehensible yet accurate specification for all 3 methods, and users are welcome to read the linked JLS chapters for more details and context.

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

  Rewording from Kevin

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Changes:
  - all: https://git.openjdk.org/jdk/pull/28684/files
  - new: https://git.openjdk.org/jdk/pull/28684/files/5fd09962..8dc4e31e

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=28684&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=28684&range=02-03

  Stats: 10 lines in 1 file changed: 0 ins; 0 del; 10 mod
  Patch: https://git.openjdk.org/jdk/pull/28684.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/28684/head:pull/28684

PR: https://git.openjdk.org/jdk/pull/28684