Add more constants for dwarf flags

[gavrilikhin-d]

Is your feature request related to a problem? Please describe.
There is no enum for LLVMDWARFTypeEncoding (alias for unsigned int) which corresponds to DW_ATE_*

Describe the solution you'd like
Add something like DIFlagsConstants for more dwarf flag enums

Describe possible drawbacks to your solution
There are several dwarf standarts, which may be bothersome to maintain. However, most users need only DWARF 4 and DWARF 5. The later came live in 2017, so there shouldn't be many updates too.

[edg-l]

https://dwarfstd.org/doc/DWARF5.pdf#section.7.8

[edg-l]

llvm/llvm-project#84456