Fix arm64 prolog generation for register masks with holes. (dotnet/coreclr#21395)

Fix arm64 prolog generation for register masks with holes. (dotnet/coreclr#21395)

* Check that `genSaveCalleeSavedRegistersHelp` doesn't accept `REG_LR`.

There are two callers and both save `LR` with `FP` before calling this helper.
In case if somebody calls this function wth`REG_LR` it won't work because unwinding info doesn't expect holes in the reg pairs.

* Extract `genPushOrPopCalleeSavedRegisters`.

It will be used for both float and int types.

* Extend `genSaveCaleeSavedRegisterGroup` to support float.

The previous version was a copy-paste with an additional case for `REG_LR` that was unreachable. Fix that.

* Use `genSaveCaleeSavedRegisterGroup` for floats.

* Extract `genRestoreCaleeSavedRegisterGroup`.

It will be used for both int and float groups.

* Prepare `genPopCalleeSavedRegisters` to work with float.

* Use `genRestoreCaleeSavedRegisterGroup` for float.

* Check that `genRestoreCalleeSavedRegistersHelp` doesn't restore `REG_LR`.

Both callers do it later.

* Extract `CheckSPOffset`.

and move it out of loops because it works only before the first save intruction.

* Format `genRestoreCaleeSavedRegisterGroup` as `genSaveCalleeSavedRegistersHelp`.

* Extract `buildRegPairsStack` from `genSaveCaleeSavedRegisterGroup` and `genRestoreCaleeSavedRegisterGroup`.

Build a stack of registers that we want to save/restore and then iterate over it doing the actual saving/restoring.

* Extract `GetSlotSizeForRegsInMask`.

* Tolerate holes in arm64 prolog/epilog register masks.

Fixes dotnet/coreclr#21363

* Reenable the test.

* Add new methods headers.

* Fix typos.

* Do not use non-const references.

* Describe `buildRegPairsStack` better.

* Change signature of `buildRegPairsStack` to avoid copyings of big structs.

* Return the logic for `RBM_LR`.

For future use.

* Clean-up some unused variables.

* Fix comments.

* Get rid of file-level functions.

* Make new methods static.

Commit migrated from https://github.com/dotnet/coreclr/commit/a9ceb1534e5a205bc1b56d0c097595ef8c2ff7f6