Map generic formal inputs in generated globals

[truemagic-coder]

Fixes #62.

GNATprove can miscompute generated Global contracts when a generic formal object of mode in is used inside an instance. When the generated contract is queried outside the instance, the instance-local constant can escape instead of being mapped back to the object referenced by the generic actual, resulting in an incorrect Global diagnostic and Program_Error.

This PR:

• maps generic formal in objects in generated Proof_Ins and Inputs back to their actual expressions;
• uses the same generic-formal mapping already applied to explicit Global contracts;
• adds the original reproducer as a regression test;
• adds nearby cases covering literal, constant, and in out generic actuals;
• documents the generated-contract behavior.

Verification

The exact submitted commit was independently verified with FalseGreen against a frozen verification contract.

• the modified gnat2why dependency closure was rebuilt from source with prior build outputs removed;
• verification used only the newly source-built gnat2why;
• 2/2 original-reproducer and 9/9 nearby proof obligations were discharged;
• 0 unproved or justified obligations;
• 0 SARIF errors and 0 unknown warnings;
• exactly two unrelated warnings matched the frozen allowlist;
• 2/2 verification criteria passed;
• verified source: 92565c8f0e744c4df2d4228ae0309ea9791e377a.

The verification is scoped to these criteria and does not claim broader correctness of GNATprove. Because a matching internal GNAT frontend for current master is not publicly available, the source-built verification used the public fsf-16 source-equivalent target while binding the submitted product files to the exact commit above.

Assisted-by: Codex

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