RFR: 8291801: IGV: Broken button "Hide graphs which are the same as the previous graph"

[Koichi Sakata]

This pull request makes the "Hide graphs..." button working.

The parser for bgv files, `BinaryParaser` class, enables the "hide graphs" function. But the xml parser, `Parser` class, doesn't have any code about the function. So I wrote code by referring to BinaryParser class.

# Tests

I tested manually. Screenshots are as follows.

<img width="1175" alt="スクリーンショット 2022-09-27 16 52 16" src="https://user-images.githubusercontent.com/60008/192467385-328b8298-9055-484d-813d-1c50200e2239.png">

In this case, there are 13 graphs and 10 graphs from "After Parsing" to "Before matching" are the same. So only 4 graphs are shown after we push the button. 

<img width="1175" alt="スクリーンショット 2022-09-27 16 52 23" src="https://user-images.githubusercontent.com/60008/192467331-fbeb4911-460d-476c-9445-098805c39d27.png">

Pushing it again or opening the graph that is hidden in the view restores the view to its original state. I attached [the graph file that I used in the test](https://github.com/openjdk/jdk/files/9653179/hello.zip).

Furthermore, I added a test method for the class I changed. Running `mvn test` command was successful.

# Concerns

I'm concerned about the equivalence of 2 graphs. I regard them as the same graphs when all fields in `InputGraph` class are equal. But in the test class, 2 graphs are equal when nodes, edges, blocks and blocks of each `InputNode` are equal. Here is an extract of the test code.


// src/utils/IdealGraphVisualizer/Data/src/test/java/com/sun/hotspot/igv/data/Util.java

    public static void assertGraphEquals(InputGraph a, InputGraph b) {

        if(!a.getNodesAsSet().equals(b.getNodesAsSet())) {
            fail();
        }

        if (!a.getEdges().equals(b.getEdges())) {
            fail();
        }

        if (a.getBlocks().equals(b.getBlocks())) {
            fail();
        }

        for (InputNode n : a.getNodes()) {
            assertEquals(a.getBlock(n), b.getBlock(n));
        }
    }


But opening a graph is very slow when I compare blocks of each InputNode. So I didn't add that comparison in `isSameContent` method.

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

Commit messages:
 - Remove extra whitespaces
 - Improve the test
 - Add the test method
 - Remove extra code
 - Fix the broken button "Hide graphs which are the same as the previous graph" in IGV

Changes: https://git.openjdk.org/jdk/pull/10440/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=10440&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8291801
  Stats: 55 lines in 4 files changed: 54 ins; 1 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/10440.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10440/head:pull/10440

PR: https://git.openjdk.org/jdk/pull/10440