Initialize the spark tool of GraphAr and implement the Info and IndexGenerator

[acezen]

Proposed changes

These changes initialize the code base of GraphAr spark tool and implement the Info classes for spark tool.

• initialize the code base of spark tool
• add GraphInfo, EdgeInfo and VertexInfo
• add related unit tests for info classes
• integrate to CI

Types of changes

What types of changes does your code introduce to GraphAr?
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• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation Update (if none of the other choices apply)

Checklist

Put an x in the boxes that apply. You can also fill these out after creating the PR. If you're unsure about any of them, don't hesitate to ask. We're here to help! This is simply a reminder of what we are going to look for before merging your code.

• I have read the CONTRIBUTING doc
• I have signed the CLA
• Lint and unit tests pass locally with my changes
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)

Further comments

Fixed issue #32

[acezen]

@lixueclaire any review comments?

[lixueclaire]

I think "GetDirPath" (for VertexInfo) and "GetAdjListDirPath"/"GetAdjListOffsetDirPath"/"GetPropertyDirPath" (for EdgeInfo) could be added for aligning with C++ SDK

[acezen]

I think "GetDirPath" (for VertexInfo) and "GetAdjListDirPath"/"GetAdjListOffsetDirPath"/"GetPropertyDirPath" (for EdgeInfo) could be added for aligning with C++ SDK

The Dir-related methods have been updated.

[lixueclaire]

It looks ready for merging~

[lixueclaire]

I'm not sure if "adj_list_type" is necessary as a input parameter for this function, also consider the functions:
def getPropertyType(property_name: String): GarType.Value
def isPrimaryKey(property_name: String): Boolean
def getPrimaryKey(): String

[acezen]

emm, you are right. adj_list_type should be include in these functions and the c++ Info class also need to updated.
This pull request can aligned to c++ at first and I will open an issue for these change and solved it as soon as possible.