[lldb][AArch64] Correctly invalidate svg when vg is written (#140875)

Recently the Linux Kernel has fixed a bunch of issues in SME support and
while testing that, I found two tests failing:
FAIL: test_za_register_dynamic_config_main_disabled
(TestZAThreadedDynamic.AArch64ZAThreadedTestCase)
FAIL: test_za_register_dynamic_config_main_enabled
(TestZAThreadedDynamic.AArch64ZAThreadedTestCase)

These tests write to vg during streaming mode from lldb and expect to
see that za has been resized to match it. Instead, it was unavailable.
lldb-server was sending the correct amount of data but lldb client was
expecting the old size.

Turns out that instead of a write to vg invalidating svg, it was
invalidating... something else. I'm still not sure how these tests ever
worked but with this one line fix, they pass again.

I did not see this issue with SVE or streaming SVE Z registers because
those always resize using the value of vg, and vg always has the value
we just wrote.

(remember that vg is the vector length of the **current** mode, not of
non-streaming mode, whereas svg is the vector length of streaming mode,
even if you are currently in non-streaming mode)

Author: DavidSpickett

lldb/source/Plugins/Process/Utility/RegisterInfoPOSIX_arm64.cpp

@@ -425,8 +425,7 @@ void RegisterInfoPOSIX_arm64::AddRegSetSME(bool has_zt) {
   //
   // This must be added now, rather than when vg is defined because SME is a
   // dynamic set that may or may not be present.
-  static uint32_t vg_invalidates[] = {sme_regnum + 1 /*svg*/,
-                                      LLDB_INVALID_REGNUM};
+  static uint32_t vg_invalidates[] = {GetRegNumSMESVG(), LLDB_INVALID_REGNUM};
   m_dynamic_reg_infos[GetRegNumSVEVG()].invalidate_regs = vg_invalidates;
 }