Add support for schema providers for generic classes

[tilgalas]

Permits to infer schemas and row conversion functions for generic classes for schema providers extending GetterBasedSchemaProvider, see new test cases for examples of such inference. The PR is mostly about passing on the TypeDescriptors where previously the mechanism used raw Classes, and making use of them to resolve generic type variables to concrete types.

This change was discussed in this design doc's section called Generic Types

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[tilgalas]

Run Java PreCommit

[tilgalas]

Run Java PreCommit

[chamikaramj]

assign set of reviewers

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[tilgalas]

closing the PR to split it into smaller ones