Escape Reserved Keywords in Codegen [1/X]

[AnthonyMDev]

This PR addresses the primary issue encountered in #2424. There is more work to be done on other types that surfaced during researching this bug.

This PR:

• Escapes swift reserved keywords in Field Accessors names
• Escapes swift reserved keywords in Test Mock property names
• Disallows certain field names entirely and Validate them in frontend
• Fixes automatic uppercasing of type names to uppercase the first actual letter.
  • for eg. on fields named _test or 5thElement
• Adds _SelectionSet suffix to generated selection set names that conflict

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