OpenVINOEncapsulation: map float16/bfloat16/bool (char) OV dtypes (microsoft#2559)

## Problem

`OpenVINOEncapsulation` builds the `EPContext` ONNX by mapping each
OpenVINO model input/output element type to an ONNX `TensorProto` dtype
via `openvino_to_onnx_dtype[str(element_type)...]`. The map was missing
the OpenVINO string spellings for several common types:

- fp16 stringifies as `float16` (only `f16` was mapped)
- bf16 as `bfloat16` (only `bf16`)
- ONNX `BOOL` round-trips through OpenVINO as `char`

As a result, encapsulating an **fp16 model** (e.g. an LLM decoder) or
any model with a **boolean mask** input crashes:

```
File ".../openvino/encapsulation.py", line 181, in _run_single_target
    inputs.append(helper.make_tensor_value_info(name, onnx_dtype, shape_list))
TypeError: 'NoneType' object cannot be interpreted as an integer
```

(`onnx_dtype` is `None` because the lookup missed.)

## Fix

Add the missing aliases: `float16` → `FLOAT16`, `bfloat16` → `BFLOAT16`,
`char` → `BOOL`.

## Validation

With this fix, `OpenVINOConversion` → `OpenVINOEncapsulation`
successfully produces `EPContext` ONNX models for all four components of
a multimodal fp16 INT4 decoder+encoders package (Gemma 4 E2B, built via
`MobiusBuilder` → `OnnxKQuantQuantization` → `MatMulNBitsToQDQ` →
OpenVINO 2026.3), including the audio encoder's boolean
`input_features_mask`. Before the fix, fp16 inputs failed immediately
and the boolean-mask encoder failed with the same `NoneType` error.

Signed-off-by: Justin Chu <11205048+justinchuby@users.noreply.github.com>
Co-authored-by: Justin Chu <11205048+justinchuby@users.noreply.github.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: justinchuby

olive/passes/openvino/encapsulation.py

@@ -29,7 +29,9 @@ class OpenVINOEncapsulation(Pass):
         "f64": TensorProto.DOUBLE,
         "float64": TensorProto.DOUBLE,
         "f16": TensorProto.FLOAT16,
+        "float16": TensorProto.FLOAT16,
         "bf16": TensorProto.BFLOAT16,
+        "bfloat16": TensorProto.BFLOAT16,
         "i8": TensorProto.INT8,
         "int8_t": TensorProto.INT8,
         "i16": TensorProto.INT16,
@@ -48,6 +50,7 @@ class OpenVINOEncapsulation(Pass):
         "uint64_t": TensorProto.UINT64,
         "bool": TensorProto.BOOL,
         "boolean": TensorProto.BOOL,
+        "char": TensorProto.BOOL,
         # Add more if needed
     }