cmake: fix Find module and package names

- fix BearSSL warning about name mismatch.
- fix Nettle Find module not found on Linux.
- tidy-up: drop quotes from a package name.

Package names must match case-sensitively to work on all platforms:
- `find_package(<NAME> ...)` in `CMakeLists.txt`.
- `CMake/Find<NAME>.cmake` filenames.
- `find_package_handle_standard_args(<NAME> ...` in Find modules.
- `message(STATUS "Found <NAME> ...` in Find modules.
  (to match the message shown by `find_package_handle_standard_args()`)

Closes #14599

CMake/FindBearSSL.cmake

@@ -45,7 +45,7 @@ find_path(BEARSSL_INCLUDE_DIR NAMES "bearssl.h")
 find_library(BEARSSL_LIBRARY NAMES "bearssl")
 
 include(FindPackageHandleStandardArgs)
-find_package_handle_standard_args(BEARSSL
+find_package_handle_standard_args(BearSSL
   REQUIRED_VARS
     BEARSSL_INCLUDE_DIR
     BEARSSL_LIBRARY

CMake/FindNettle.cmake

@@ -44,7 +44,7 @@ endif()
 
 if(NETTLE_FOUND)
   set(NETTLE_LIBRARIES ${NETTLE_LINK_LIBRARIES})
-  message(STATUS "Found nettle (via pkg-config): ${NETTLE_INCLUDE_DIRS} (Found version \"${NETTLE_VERSION}\")")
+  message(STATUS "Found Nettle (via pkg-config): ${NETTLE_INCLUDE_DIRS} (Found version \"${NETTLE_VERSION}\")")
 else()
   find_path(NETTLE_INCLUDE_DIR NAMES "nettle/sha2.h")
   find_library(NETTLE_LIBRARY NAMES "nettle")
@@ -64,7 +64,7 @@ else()
   endif()
 
   include(FindPackageHandleStandardArgs)
-  find_package_handle_standard_args("nettle"
+  find_package_handle_standard_args(Nettle
     REQUIRED_VARS
       NETTLE_INCLUDE_DIR
       NETTLE_LIBRARY

CMakeLists.txt

@@ -615,7 +615,7 @@ if(CURL_USE_GNUTLS)
   if(NOT GNUTLS_FOUND)
     find_package(GnuTLS REQUIRED)
   endif()
-  find_package(nettle REQUIRED)
+  find_package(Nettle REQUIRED)
   set(_ssl_enabled ON)
   set(USE_GNUTLS ON)
   list(APPEND CURL_LIBS ${GNUTLS_LIBRARIES} ${NETTLE_LIBRARIES})