refactor: Rename cmake files and definitions (#5975)

Per XLS-0095, we are taking steps to rename ripple(d) to xrpl(d).

This change updates the CMake files and definitions therein, plus a handful of related modifications. Specifically, the compiler files are renamed from `RippleXXX.cmake` or `RippledXXX.cmake` to `XrplXXX.cmake`, and any references to `ripple` and `rippled` (with or without capital letters) are renamed to `xrpl` and `xrpld`, respectively. The name of the binary, currently `rippled`, remains unchanged and will be updated in a separate PR. This change is purely cosmetic and does not affect the functioning of the binary.

cmake/XrplValidatorKeys.cmake

@@ -0,0 +1,20 @@
+option (validator_keys "Enables building of validator-keys tool as a separate target (imported via FetchContent)" OFF)
+
+if (validator_keys)
+  git_branch (current_branch)
+  # default to tracking VK master branch unless we are on release
+  if (NOT (current_branch STREQUAL "release"))
+    set (current_branch "master")
+  endif ()
+  message (STATUS "Tracking ValidatorKeys branch: ${current_branch}")
+
+  FetchContent_Declare (
+    validator_keys
+    GIT_REPOSITORY https://github.com/ripple/validator-keys-tool.git
+    GIT_TAG        "${current_branch}"
+  )
+  FetchContent_MakeAvailable(validator_keys)
+  set_target_properties(validator-keys PROPERTIES RUNTIME_OUTPUT_DIRECTORY "${CMAKE_BINARY_DIR}")
+  install(TARGETS validator-keys RUNTIME DESTINATION ${CMAKE_INSTALL_BINDIR})
+
+endif ()