Add deprecate executable metadata update simd

proposals/xxxx-deprecate-executable-meta-update-in-bpf-loader.md

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+---
+simd: 'xxxx'
+title: Deprecate executable account metadata update during bpf program deployment
+authors:
+  - Haoran Yi
+category: Standard
+type: Core
+status: Draft
+created: 2023-12-13
+feature: https://github.com/solana-labs/solana/issues/33970
+---
+
+## Summary
+
+Add a new feature to deprecate executable account metadata update during bpf
+program deployment.
+
+## Motivation
+
+We want to deprecate the usage of *executable* metadata on account for program
+runtime. The new variant of Bpf loader (i.e. V2, V4 etc.) no longer requires
+*executable* metadata. However, during the program deployment, bpf loader still
+updates *executable* account metadata, which is not necessary.
+
+Therefore, as we are migrating from the old Bpf loader to the new Bpf loader, we
+are going to add a feature to deprecate executable account metadata update
+during bpf program deployment, so that we can activate the feature and deprecate
+*executable* metadata in program runtime for the new kind of Bpf loaders.
+
+
+## Alternatives Considered
+
+None
+
+## New Terminology
+
+None
+
+## Detailed Design
+
+When the feature - "deprecate executable account metadata update" is activated,
+the bpf loader will no longer mark *executable* metadata to true after
+program deployment.
+
+The PR for this work is at https://github.com/solana-labs/solana/pull/34194
+
+## Impact
+
+1. People should no longer reply on *executable* metadata on the account. Instead,
+   they can use an exported *fn is_executable(&account)* from solana sdk.
+
+
+## Security Considerations
+
+Because when the feature is activated, we should have already migrated to Bpf
+loader V2. Bpf loader V1 program deployment should have already been disabled
+(https://github.com/solana-foundation/solana-improvement-documents/pull/93).
+
+Account's owner and bpf loader metadata stored in account's data should
+correctly tell whether an account is executable.
+
+A small concern is that we may miss places in the code that still relies on
+account *executable*. However, with good testing, we should be able to cover all
+of them. And a fix for this should be not hard.
+
+## Backwards Compatibility
+
+Incompatible.