[lldb] Support non-pointer implicit this/self in GetValueForVariableExpressionPath

The `frame variable` command supports an implicit `this`/`self`, allowing a
user to run `v some_field` instead of `v this->some_field`. However, some
languages have non-pointer `this`/`self` types (for example, Swift).

This change adds support for non-pointer implicit `this`/`self`. This is done
by consulting the type of the instance variable. If the type is known to be
non-pointer, the dot operator is used instead of the arrow operator.

The C language of families each have a pointer instance type, which makes
testing of this difficult. Tests for this feature will be done in the Swift
downstream fork, as Swift's `self` is a non-pointer (reference) type.

rdar://82095148

Reviewed By: aprantl

Differential Revision: https://reviews.llvm.org/D127605