Remove unused code and unnecessary function calls, optimize global
variable search.
Add more test cases.

As a preliminary to making DIL the default implementation for
 'frame var', ran check-lldb forcing 'frame var' to always use DIL, 
and discovered a few failing tests. This fixes most of them. The only
remaining failing test is TestDAP_evaluate.py, which now passes
a test case that the test says should fail (still investigating this).

Changes in this PR:
- Sets correct VariableSP, as well as returning ValueObjectSP (needed
for several watchpoint tests).
- Updates error messages, when looking up members, to match what the
rest of LLDB expects. Also update appropriate DIL tests to expect the
updated error messages.
- Updates DIL parser to look for and accept "(anonymous namespace)::" at
the front of a variable name.

This updates the DIL implementation to handle smart pointers (accessing
field members and dereferencing) in the same way the current 'frame
variable' implementation does. It also adds tests for handling smart
pointers, as well as some additional DIL tests.

Reapply #138551 with an xfailed test on Windows

Add the arrow and period operators, allowing DIL to find and access
member fields.

Reverts llvm/llvm-project#138551

Add the Data Inspection Language (DIL) implementation pieces for
handling plain local and global variable names.

See https://discourse.llvm.org/t/rfc-data-inspection-language/69893 for
information about DIL.

This change includes the basic AST, Lexer, Parser and Evaluator pieces,
as well as some tests.