Add support for BOM priotization

[tharakadesilva]

With the current code, if multiple BOMs have the same coords, the coordinates would be resolved through all the BOMs when we try to resolve the artifact versions. ~When two or more versions were present, Maven resolver would resort to the lower version (IIUC, default Maven behavior).~ The issue was that the set that was created was not ordered, so it would not give priority to the first defined BOM.

~With these changes, we will ignore the artifact if it was previously found, thus giving priority to the BOM that was defined first.~

We now have a LinkedHashSet that will maintain the ordering so that the BOMs will be given priority based on the order they were defined.

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Closes https://github.com/bazelbuild/rules_jvm_external/issues/1146.

[tharakadesilva]

I am yet to add any tests, will do that once I've received the go-ahead on the strategy.

[tharakadesilva]

@cheister for the tests, I am thinking of something like this:

• Will be placed in MavenResolverTest.java file.
• Do a MavenRepo.create().
• Add two BOMs to it with the same artifact at two different versions.
• Add a coordinate without version.
• See if the version from the first defined BOM resolves.

Do you have any thoughts on this?

[cheister]

Do you have any thoughts on this?

That sounds good to me