Add build/test dockerfile support for hexagon dsp

Shichuang Chenrequested to merge
ShichuangChen/eigen:add_build_for_hexagon_dsp into master

Reference issue

N/A

What does this implement/fix?

Add hexagon environment dockerfile for qualcomm hexagon DSP build/test. cmake/HexagonToolchain.cmake is copied from !1375 (merged). Currently, it need qualcomm account to get the Hexagon SDK to build/test.

Additional information

We noticed there are some tests failed passed, some of them are related to qfloat32 different with standard IEEE-754 float, some of them need to further check. Setting up hexagon build/test environment firstly, so everyone can build/test with standard Hexagon SDK.

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