RFR: 8092379: GridPane should not render extra gaps when entire rows or columns are unmanaged [v2]

[John Hendrikx]

> This fixes a long standing bug with `GridPane` where unmanaged nodes would still result in gaps being added between rows/columns even though nothing is rendered there.  Take the following grid where dashes and pipes represent the vgaps and hgaps:
> 
> |            |0| |1|
> |--------|---|---|---|
> |0  |A|||B|
> |    |-|||-|
> |1  |C|||D|
> |    |-|||-|
> |2  |E|||F|
> 
> Now, when both C and D are set to unmanaged (and invisible) the grid will **still** render the gaps:
> 
> |            |0| |1|
> |--------|---|---|---|
> |0  |A|||B|
> |    |-|||-|
> |1  |||||
> |    |-|||-|
> |2  |E|||F|
> 
> Instead it should collapse the gap between row 0 and 2:
> 
> |            |0| |1|
> |--------|---|---|---|
> |0  |A|||B|
> |    |-|||-|
> |2  |E|||F|
> 
> There are at least two relevant issues in JBS:
> - A request to let the user show and hide rows and columns: https://bugs.openjdk.org/browse/JDK-8136901
>   - This can now be done by setting the relevant row/columns items to unmanaged without having to restructure the grid (assuming the complaint was that otherwise there'd be visible extra gaps for each hidden row)
> - A request for another mode to skip gaps when entire rows/columns are unmanaged: https://bugs.openjdk.org/browse/JDK-8092379
>   - This should not be a mode, but the standard, as unmanaged nodes should not affect the outcome of the grid layout
> 
> Screenshots
> 
> Simple application which can hide row 3:
> 
> <img width="443" height="491" alt="image" src="https://github.com/user-attachments/assets/0342dba3-cd1c-4d9e-9451-e9c8c628b2e2" />
> 
> Correct behavior when row 3 is hidden:
> 
> <img width="443" height="408" alt="image" src="https://github.com/user-attachments/assets/c7c54414-6a03-43e4-b733-21d0b251d729" />
> 
> Behavior before this fix (note the double gap **and** extra grid line):
> 
> <img width="443" height="453" alt="image" src="https://github.com/user-attachments/assets/f357e68a-e950-42e7-890b-91a78e194dd0" />

John Hendrikx has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains two additional commits since the last revision:

 - Merge branch 'openjdk:master' into feature/grid-proper-gaps
 - When all nodes starting in a row or column are unmanaged, skip gap

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

Changes:
  - all: https://git.openjdk.org/jfx/pull/1990/files
  - new: https://git.openjdk.org/jfx/pull/1990/files/8155fc61..9f2f95df

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jfx&pr=1990&range=01
 - incr: https://webrevs.openjdk.org/?repo=jfx&pr=1990&range=00-01

  Stats: 3630 lines in 126 files changed: 2903 ins; 302 del; 425 mod
  Patch: https://git.openjdk.org/jfx/pull/1990.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1990/head:pull/1990

PR: https://git.openjdk.org/jfx/pull/1990