[lldb] Also recognize DWARF UTF base types using their size

Summary:
The D programming language has 'char', 'wchar', and 'dchar' as base types,
which are defined as UTF-8, UTF-16, and UTF-32, respectively.

It also has type constructors (e.g. 'const' and 'immutable'),
that leads to D compilers emitting DW_TAG_base_type with DW_ATE_UTF
and name 'char', 'immutable(wchar)', 'const(char)', etc...

Before this patch, DW_ATE_UTF would only recognize types that
followed the C/C++ naming, and emit an error message for the rest, e.g.:
```
error: need to add support for DW_TAG_base_type 'immutable(char)'
encoded with DW_ATE = 0x10, bit_size = 8
```

The code was changed to check the byte size first,
then fall back to the old name-based check.

Reviewers: clayborg, labath

Reviewed By: labath

Subscribers: labath, lldb-commits

Tags: #lldb

Differential Revision: https://reviews.llvm.org/D79559