[WinEH][ARM64] Split Unwind Info for Fucntions Larger than 1MB

Create function segments and emit unwind info of them.

A segment must be less than 1MB and no prolog or epilog is splitted between two
segments.

This patch should generate correct, though not optimal, unwind info for large
functions. Currently it only generate pacted info (.pdata) only for functions
that are less than 1MB (single-segment functions). This is NFC from before this
patch.

The next step is to enable (.pdata) only unwind info for the first segment or
segments that have neither prolog or epilog in a multi-segment function.

Another future work item is to further split segments that require more than 255
code words or have more than 65535 epilogs.

Reference:
https://docs.microsoft.com/en-us/cpp/build/arm64-exception-handling#function-fragments

Differential Revision: https://reviews.llvm.org/D130049