[AArch64] Replace LLVM IR function attributes for PSTATE.ZA. (#79166)

Since https://github.com/ARM-software/acle/pull/276 the ACLE
defines attributes to better describe the use of a given SME state

[AArch64] Replace LLVM IR function attributes for PSTATE.ZA. (#79166)

Since https://github.com/ARM-software/acle/pull/276 the ACLE
defines attributes to better describe the use of a given SME state.

Previously the attributes merely described the possibility of it being
'shared' or 'preserved', whereas the new attributes have more semantics
and also describe how the data flows through the program.

For ZT0 we already had to add new LLVM IR attributes:
* aarch64_new_zt0
* aarch64_in_zt0
* aarch64_out_zt0
* aarch64_inout_zt0
* aarch64_preserves_zt0

We have now done the same for ZA, such that we add:
* aarch64_new_za (previously `aarch64_pstate_za_new`)
* aarch64_in_za (more specific variation of `aarch64_pstate_za_shared`)
* aarch64_out_za (more specific variation of `aarch64_pstate_za_shared`)
* aarch64_inout_za (more specific variation of
`aarch64_pstate_za_shared`)
* aarch64_preserves_za (previously `aarch64_pstate_za_shared,
aarch64_pstate_za_preserved`)

This explicitly removes 'pstate' from the name, because with SME2 and
the new ACLE attributes there is a difference between "sharing ZA"
(sharing
the ZA matrix register with the caller) and "sharing PSTATE.ZA" (sharing
either the ZA or ZT0 register, both part of PSTATE.ZA with the caller).

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[AArch64][SME2] Preserve ZT0 state around function calls (#78321)

If a function has ZT0 state and calls a function which does not
preserve ZT0, the caller must save and restore ZT0 around the call.

[AArch64][SME2] Preserve ZT0 state around function calls (#78321)

If a function has ZT0 state and calls a function which does not
preserve ZT0, the caller must save and restore ZT0 around the call.
If the caller shares ZT0 state and the callee is not shared ZA, we must
additionally call SMSTOP/SMSTART ZA around the call.

This patch adds new AArch64ISDNodes for spilling & filling ZT0.
Where requiresPreservingZT0 is true, ZT0 state will be preserved
across a call.

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[AArch64] NFC: Simplify discombobulating 'requiresSMChange' interface (#78703)

Having it return a `std::optional<bool>` is unnecessarily confusing.
This patch changes it to a simple 'bool'.

This

[AArch64] NFC: Simplify discombobulating 'requiresSMChange' interface (#78703)

Having it return a `std::optional<bool>` is unnecessarily confusing.
This patch changes it to a simple 'bool'.

This patch also removes the 'BodyOverridesInterface' operand because
there is only a single use for this which is easily rewritten.

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[AArch64][SME2] Add ZT0 attributes to SMEAttrs (#77607)

This patch extends SMEAttrs to interpret the following new attributes,
which are mutually exclusive and apply to SME2 only:
- aarch64_sme_

[AArch64][SME2] Add ZT0 attributes to SMEAttrs (#77607)

This patch extends SMEAttrs to interpret the following new attributes,
which are mutually exclusive and apply to SME2 only:
- aarch64_sme_zt0_in (ZT0_In)
- aarch64_sme_zt0_out (ZT0_Out)
- aarch64_sme_zt0_inout (ZT0_InOut)
- aarch64_sme_zt0_new (ZT0_New)
- aarch64_sme_zt0_preserved (ZT0_Preserved)

ZT0_In, ZT0_Out, ZT0_InOut & ZT0_Preserved are all considered to share
ZT0. These attributes will be required by later patches to determine
if ZT0 should be preserved around function calls, or cleared on entry
to the function.

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[AArch64][SME] NFC: Rename hasNewZAInterface to hasNewZABody.

__arm_new_za is a declaration attribution, not a type attribute,
and is therefore not part of the interface of a function.

[AArch64][SME] Add utility class for handling SME attributes.

This patch adds a utility class that will be used in subsequent patches
for parsing the function/callsite attributes and determining whe

[AArch64][SME] Add utility class for handling SME attributes.

This patch adds a utility class that will be used in subsequent patches
for parsing the function/callsite attributes and determining whether
changes to PSTATE.SM are needed, or whether a lazy-save mechanism is
required.

It also implements some of the restrictions on the SME attributes
in the IR Verifier pass.

More details about the SME attributes and design can be found
in D131562.

Reviewed By: david-arm, aemerson

Differential Revision: https://reviews.llvm.org/D131570

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