[IR2Vec] Add embeddings mode to llvm-ir2vec tool

[svkeerthy]

Add embedding generation functionality to the llvm-ir2vec tool, complementing the existing triplet generation mode.

This change completes the IR2Vec tool by adding the embedding generation functionality, which was previously mentioned as a TODO item. The tool now supports both triplet generation for vocabulary training and embedding generation using a trained vocabulary.

[svkeerthy]

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• [IR2Vec] Add embeddings mode to llvm-ir2vec tool #147844 👈 (View in Graphite)
• [IR2Vec] Add llvm-ir2vec tool for generating triplet embeddings #147842
• [NFC][IR2Vec] Exposing helpers in IR2Vec Vocabulary #147841
• [NFC][IR2Vec] Minor refactoring of opcode access in vocabulary #147585
• [IR2Vec] Restructuring Vocabulary #145119
• [IR2Vec] Add out-of-place arithmetic operators to Embedding class #145118
• [NFC][IR2Vec] Increasing tolerance in approximatelyEquals() of Embedding  #145117
• [IR2Vec] Simplifying creation of Embedder #143999
• [IR2Vec] Scale embeddings once in vocab analysis instead of repetitive scaling #143986
• [MLGO][IR2Vec] Integrating IR2Vec with MLInliner #143479 : 1 other dependent PR (#144139 )
• [IR2Vec] Consider only reachable BBs and non-debug instructions #143476
• [IR2Vec] Minor vocab changes and exposing weights #143200
• [IR2Vec] Exposing Embedding as an data type wrapped around std::vector<double> #143197
• main

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