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

src/test/CMakeLists.txt

@@ -213,4 +213,4 @@ endfunction()
 
 add_all_test_targets()
 
-install_binary_component(test_bitcoin)
+install_binary_component(test_bitcoin INTERNAL)