naming: shm → shared_memory — 'shm' is a Unix clipping, not an acronym

Per docs/coding-standards.md (no Unix-abbreviation exception): syscalls
shared_memory_create/map/physical, kernel SharedMemoryObject + handlers,
runtime.shared_memory (library/runtime/shared-memory.zig), the
shared-memory-server/-client test services, the shared-memory QEMU case,
and docs incl. vdso.md's danos_shared_memory_*. 87/87 QEMU tests pass.

library/runtime/runtime.zig

@@ -38,9 +38,9 @@ pub const device = @import("device.zig");
 pub const dma = @import("dma.zig");
 
 /// Shared cacheable memory: create a region + capability, pass the capability to another
-/// process (an `ipc_call` send_cap), map the same pages there. See library/runtime/shm.zig
+/// process (an `ipc_call` send_cap), map the same pages there. See library/runtime/shared-memory.zig
 /// and docs/display-v2.md.
-pub const shm = @import("shm.zig");
+pub const shared_memory = @import("shared-memory.zig");
 
 /// USB class-driver client: open a device on the xHCI bus and drive it
 /// (control / interrupt / bulk transfers). See library/runtime/usb.zig.

library/runtime/shared-memory.zig

@@ -1,7 +1,7 @@
-//! User-space shared memory: `shm_create` / `shm_map`. A process creates a shareable,
+//! User-space shared memory: `shared_memory_create` / `shared_memory_map`. A process creates a shareable,
 //! zeroed, cacheable RAM region and gets back a pointer plus a **capability handle**; it
 //! passes that handle to another process as an `ipc_call` send_cap, and the receiver
-//! `shm_map`s it to map the same physical pages. The kernel primitive under the display
+//! `shared_memory_map`s it to map the same physical pages. The kernel primitive under the display
 //! compositor↔native-driver and app↔compositor surface paths (docs/display-v2.md). The
 //! generalization of capability passing from endpoints to memory objects.
 
@@ -30,7 +30,7 @@ pub fn create(len: usize) ?Region {
     asm volatile ("syscall"
         : [rax] "={rax}" (rax),
           [rdx] "={rdx}" (rdx),
-        : [n] "{rax}" (@intFromEnum(abi.SystemCall.shm_create)),
+        : [n] "{rax}" (@intFromEnum(abi.SystemCall.shared_memory_create)),
           [a0] "{rdi}" (len),
         : .{ .rcx = true, .r11 = true, .memory = true });
     if (failed(rax)) return null;
@@ -41,7 +41,7 @@ pub fn create(len: usize) ?Region {
 /// `ipc_call` send_cap) into its address space — the same physical pages the creator sees.
 /// Returns the pointer, or null on failure.
 pub fn map(handle: ipc.Handle) ?[*]u8 {
-    const r = sc.systemCall1(.shm_map, handle);
+    const r = sc.systemCall1(.shared_memory_map, handle);
     if (failed(r)) return null;
     return @ptrFromInt(r);
 }
@@ -51,7 +51,7 @@ pub fn map(handle: ipc.Handle) ?[*]u8 {
 /// the region length is all a device needs — e.g. a virtio-gpu driver programming an
 /// `attach_backing`. Returns null on failure.
 pub fn physical(handle: ipc.Handle) ?usize {
-    const r = sc.systemCall1(.shm_physical, handle);
+    const r = sc.systemCall1(.shared_memory_physical, handle);
     if (failed(r)) return null;
     return r;
 }