[lldb][TypeSystemClang] Use the CXXFunctionPointerSummaryProvider for member-function...

[lldb][TypeSystemClang] Use the CXXFunctionPointerSummaryProvider for member-function pointers

With this patch member-function pointers are formatted using
`CXXFunctionPointerSummaryProvider`.

This turns,
```
(lldb) v pointer_to_member_func
(void (Foo::*)()) ::pointer_to_member_func = 0x00000000000000000000000100003f94
```
into
```
(lldb) v pointer_to_member_func
(void (Foo::*)()) ::pointer_to_member_func = 0x00000000000000000000000100003f94 (a.out`Foo::member_func() at main.cpp:3)
```

Differential Revision: https://reviews.llvm.org/D145242