RFR: 8364230: javax/swing/text/StringContent can be migrated away from using finalize [v2]

[Phil Race]

> Convert StringContent's Position usage tracking to use a WeakReference
> 
> The test that is added only implicitly tests this but I added it because of a complete lack of any test for this code.

Phil Race has updated the pull request incrementally with one additional commit since the last revision:

  8364230

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Changes:
  - all: https://git.openjdk.org/jdk/pull/26519/files
  - new: https://git.openjdk.org/jdk/pull/26519/files/f423e1d9..e37e57c2

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=26519&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=26519&range=00-01

  Stats: 10 lines in 1 file changed: 0 ins; 0 del; 10 mod
  Patch: https://git.openjdk.org/jdk/pull/26519.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/26519/head:pull/26519

PR: https://git.openjdk.org/jdk/pull/26519