Let an analysis plugin provide the decompiler ##analysis

[0verflowme]

Lets an analysis plugin act as the decompiler provider, and adds the small set of things such a provider needs from radare2 rather than reimplementing them.

Provider API

• RAnalPlugin.decompile: a callback that renders one RAnalFunction to an RCodeMeta. The best-scoring eligible plugin that has one is the provider (r_anal_decompiler_provider), and r_anal_decompile invokes it. Ties keep registration order.
• pdd [name|addr] routes to the provider before the existing sdb fallback command, so pdc? and the fallback keep working when no provider is registered.

Facts the provider consumes

• A dirty epoch on RAnalFunction and on the type database, bumped on the mutations that change typed metadata (variables, signatures, calling convention, bits, maxstack, type links, type loads). A provider uses it to know whether a cached result is stale.
• r_anal_function_get_signature_current and r_anal_function_has_address_linked_signature_current: read-only signature queries that do not trigger type loading, for use while analysis holds the lock.
• r_anal_cc_location_uses exported, case-insensitive on the register name, so a convention's roles can be matched against the registers a function touches.
• stackalloc, redzone and retmech keys in the calling convention tables, and they are cleared with the rest of the layout on redefinition.
• RBinBind.get_reloc_at and RBinBind.get_sym, so an analysis holding only the bind can ask what a relocated slot names.
• RAnalPluginAnalysisDepth: aa, aaa and aaaa tell post-analysis hooks how much work is appropriate.

Alongside

• afs prints the stored signature when one exists before formatting from variables.
• afc <cc> goes through r_anal_function_set_callconv, which validates and bumps the epoch.
• r_anal_function_delete refuses a function it does not own and honours R_ANAL_FUNCTION_DELETE_REFUSE from the delete callback.
• aaa no longer re-imports DWARF when the bin layer declined for size; the size limit was being defeated on exactly the binaries it protects.
• Plugin variable batches are validated before they touch the function and rolled back if a write fails.

Unit tests cover provider selection, the decompile wrapper and pdd routing (test_anal_decompiler), the epoch bumps (test_anal_function), and the DWARF integration test is registered in meson again.

Replaces #26646, which carried this together with the removal now in its own pull request.

[trufae]

Providing decompilers from anal is a design topic that it shouldnt be discused in a pr also this pr ships many more changes than just this thing

[0verflowme]

Agreed on both counts, and withdrawn. r2sleigh does not register as a decompiler provider any more (it answers pd:s through a core plugin), so the provider API here has no user and does not need a design discussion on our side. The facts the plugin does read from libr/anal are now separate pull requests, one idea each: #26704 (cc table keys), #26705 (RBinBind lookups), #26706 (dirty epochs), #26707 (read-only signature query), #26708 (post-analysis depth). The hardening changes that rode along here are dropped.