cmake: Move internal binaries from bin/ to libexec/

This change moves binaries that are not typically invoked directly by users
from the `bin/` directory to the `libexec/` directory in CMake installs and
binary releases. The goal is to simplify the contents of `bin/` for end users
while still making all binaries available when needed. After this change, the
binaries remaining in `bin/` are:

- bitcoin
- bitcoin-cli
- bitcoind
- bitcoin-qt
- bitcoin-tx
- bitcoin-util
- bitcoin-wallet

And the binaries that are moved to `libexec/` are:

- bench_bitcoin
- bitcoin-chainstate(*)
- bitcoin-gui(***)
- bitcoin-node(***)
- test_bitcoin(**)
- test_bitcoin-qt

(*) bitcoin-chainstate was previously missing an install rule and was actually
not installed even when it was enabled.

(**) test_bitcoin is the only libexec/ binary that is currently included in
bitcoin binary releases. The others are only installed when building from
source with relevant cmake options enabled.

(***) bitcoin-node and bitcoin-gui are not currently built by default or
included in binary releases but both of these changes are planned and
implemented in #31802

contrib/guix/libexec/codesign.sh

@@ -110,7 +110,7 @@ mkdir -p "$DISTSRC"
 
             # Apply detached codesignatures (in-place)
             signapple apply dist/Bitcoin-Qt.app codesignatures/osx/"${HOST}"/dist/Bitcoin-Qt.app
-            find "${DISTNAME}" -wholename "*/bin/*" -type f | while read -r bin
+            find "${DISTNAME}" \( -wholename "*/bin/*" -o -wholename "*/libexec/*" \) -type f | while read -r bin
             do
                 signapple apply "${bin}" "codesignatures/osx/${HOST}/${bin}.${ARCH}sign"
             done