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

cmake/module/InstallBinaryComponent.cmake

@@ -7,14 +7,19 @@ include(GNUInstallDirs)
 
 function(install_binary_component component)
   cmake_parse_arguments(PARSE_ARGV 1
-    IC                # prefix
-    "HAS_MANPAGE"     # options
-    ""                # one_value_keywords
-    ""                # multi_value_keywords
+    IC                          # prefix
+    "HAS_MANPAGE;INTERNAL"      # options
+    ""                          # one_value_keywords
+    ""                          # multi_value_keywords
   )
   set(target_name ${component})
+  if(IC_INTERNAL)
+    set(runtime_dest ${CMAKE_INSTALL_LIBEXECDIR})
+  else()
+    set(runtime_dest ${CMAKE_INSTALL_BINDIR})
+  endif()
   install(TARGETS ${target_name}
-    RUNTIME DESTINATION ${CMAKE_INSTALL_BINDIR}
+    RUNTIME DESTINATION ${runtime_dest}
     COMPONENT ${component}
   )
   if(INSTALL_MAN AND IC_HAS_MANPAGE)