[Lang] Add any()/all() functions for Matrix, move casting ops to common_ops

[KLozes]

I added any()/all() functions to Matrix to check if any/all matrix entries are non-zero. It works on float and int types. They can be called in using builtin syntax or as a method of a matrix.

any(mat) or mat.any() 
all(mat) or mat.all()

I also moved ti_int and ti_float to common ops, which allows casting of matrices with

int(mat)
float(mat)

Related issue = #1050

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[yuanming-hu]

Cool! Could you please add all(A) and any(A) to the list here https://taichi.readthedocs.io/en/latest/matrix.html#matrices? Feel free to merge once that's documented.

Meanwhile, seeing the confusing negative integer representations, I feel like we really need support for boolean types (u1) now...

[KLozes]

Thanks! I agree the the negative integers were confusing and unexpected.