[LLDB][NativePDB] Mark blocks as parsed after parsing (#157493)

After parsing blocks in a function, the blocks should be marked as
parsed for them to be dumped (see
[Function::Dump](https://github.com/llvm/llvm-project/blob/e6aefbec782dbb57f72eb0ae399ed944fe49db2e/lldb/source/Symbol/Function.cpp#L446-L447)).
As explained in
https://github.com/llvm/llvm-project/issues/114906#issuecomment-3255016266,
this happens (accidentally?) in the DIA plugin when parsing variables,
because it calls `function.GetBlock(can_create=true)` which marks blocks
as parsed. In the native plugin, this was never called, so blocks and
variables were never included in the `lldb-test symbols` output.

The `variables.test` for the DIA plugin tests this. One difference
between the plugins is how they specify the location of local variables.
This causes the output of the native plugin to be two lines per
variable, whereas the DIA plugin has one line:
```
(native):
000002C4B7593020:       Variable{0x1c800001}, name = "var_arg1", type = {0000000000000744} 0x000002C4B6CA7900 (int), scope = parameter, location = 0x00000000:
        [0x000000014000102c, 0x000000014000103e): DW_OP_breg7 RSP+8
```
```
(DIA):
000002778C827EE0:       Variable{0x0000001b}, name = "var_arg1", type = {0000000000000005} 0x000002778C1FBAB0 (int), scope = parameter, decl = VariablesTest.cpp:32, location = DW_OP_breg7 RSP+8
```
In the test, I filtered lines starting with spaces followed by `[0x`, so
we can still use `CHECK-NEXT`.

---

Another difference between the plugins is that DIA marks the `this`
pointer as artificial (equivalent to DWARF). This is done if a
variable's object kind is `ObjectPtr`
([source](https://github.com/llvm/llvm-project/blob/ab898f32c60689d1d47d0b6de66c30d3476994bb/lldb/source/Plugins/SymbolFile/PDB/SymbolFilePDB.cpp#L1050)).
As far as I know, there isn't anything in the debug info that says "this
variable is the `this` pointer" other than the name/type of a variable
and the type of the function.