[lldb/DWARF] Add support for DW_OP_implicit_value

This patch completes https://reviews.llvm.org/D83560. Now that the
compiler can emit `DW_OP_implicit_value` into DWARF expressions, lldb
needed to learn reading these opcodes for variable inspection and
expression evaluation.

This implicit location descriptor specifies an immediate value with two
operands: the length (ULEB128) followed by a block representing the value
in the target memory representation.

rdar://67406091

Differential revision: https://reviews.llvm.org/D89842



Signed-off-by: Med Ismail Bennani <medismail.bennani@gmail.com>