RFR: 8372948: Store end positions directly in JCTree [v7]

[Liam Miller-Cushon]

> This change adds a field to `JCTree` to store end positions, instead of using a separate `EndPosTable` map. See also [this compiler-dev@ thread](https://mail.openjdk.org/pipermail/compiler-dev/2025-November/032254.html).
> 
> I performed the refactoring in stages, preserving existing semantics at each step.
> 
> There are two known places where this changes existing behaviour that are reflected in changes to tests:
> 
> * `test/langtools/tools/javac/api/TestJavacTask_Lock.java` - this test asserts that calling `JavacTask#parse` first and then calling `#call` or `#parse` second will fail. The assertion that the test is currently expecting is thrown when the `EndPosTable` gets set a second time, and this change means that no longer results in an exception. If desired `JavacTask#parse` could be updated to explicitly check if it is called twice and fail, instead of indirectly relying on the `EndPosTable` for that.
> 
> * `test/langtools/tools/javac/diags/DiagnosticGetEndPosition.java` - there's a comment that 'ideally would be "0", but the positions are not fully set yet', and with the new approach the end position is available to the test, so it resolves the comment. Also the test logic didn't handle platform specific line ending variations correctly, so I updated it to work on windows now that end positions are present.

Liam Miller-Cushon has updated the pull request incrementally with one additional commit since the last revision:

  Review feedback
  
  * Improve valiation in JavacTaskImpl and revert workaround in TestJavacTask_Lock.java
  * Add an assertion to DiagnosticGetEndPosition.java
  * Update test/langtools/tools/javac/6304921/TestLog.java for EndPosTable removal

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Changes:
  - all: https://git.openjdk.org/jdk/pull/28610/files
  - new: https://git.openjdk.org/jdk/pull/28610/files/fc2f82c4..3432b139

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=28610&range=06
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=28610&range=05-06

  Stats: 9 lines in 3 files changed: 6 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/28610.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/28610/head:pull/28610

PR: https://git.openjdk.org/jdk/pull/28610