RFR: JDK-8294565: IGV: ClassCastException when clicking on an edge in the graph [v3]

[Tobias Holenstein]

> IGV crashed when the user clicked on any edge in the graph because the `select` method of the `SelectProvider` in `LineWidget.java` was faulty. 
> 
> # Implementation
> - `ActionFactory.createSelectAction` was changed to `CustomSelectAction` since it also supports to invert the selection with `Ctrl/CMD`
> - The `select` method gets called when the user clicks on an edge. `LineWidget` represents a single connection going out of a node and connecting to one or more nodes (one-to-many). `LineWidget` has a list of `Connection`'s that each represent a single link between two nodes (one-to-one). For each `connection` we collect the from/to `Vertex` (superclass for a node) and put them into a set that we then use to select the nodes that are connected to the user-clicked `LineWidget`.

Tobias Holenstein has updated the pull request incrementally with two additional commits since the last revision:

 - whitespace
   
   Co-authored-by: Andrey Turbanov <turbanoff at gmail.com>
 - whitespace
   
   Co-authored-by: Andrey Turbanov <turbanoff at gmail.com>

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Changes:
  - all: https://git.openjdk.org/jdk/pull/10760/files
  - new: https://git.openjdk.org/jdk/pull/10760/files/e326b033..cd327309

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=10760&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=10760&range=01-02

  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/10760.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10760/head:pull/10760

PR: https://git.openjdk.org/jdk/pull/10760