build(externals): rename Findopus to FindOpus

This better matches upstream's FindOpus.cmake file, and it will make
using upstream's FindOpus.cmake file easier.

externals/CMakeLists.txt

@@ -128,7 +128,7 @@ endif()
 if (YUZU_USE_BUNDLED_OPUS)
     add_subdirectory(opus EXCLUDE_FROM_ALL)
 else()
-    find_package(opus 1.3 REQUIRED)
+    find_package(Opus 1.3 REQUIRED)
 endif()
 
 # FFMpeg

externals/find-modules/FindOpus.cmake

@@ -6,12 +6,12 @@ find_package(PkgConfig)
 if (PKG_CONFIG_FOUND)
     pkg_search_module(opus IMPORTED_TARGET GLOBAL opus)
     if (opus_FOUND)
-        add_library(Opus::Opus ALIAS PkgConfig::opus)
+        add_library(Opus::opus ALIAS PkgConfig::opus)
     endif()
 endif()
 
 include(FindPackageHandleStandardArgs)
-find_package_handle_standard_args(opus
+find_package_handle_standard_args(Opus
     REQUIRED_VARS
         opus_LINK_LIBRARIES
         opus_FOUND

externals/opus/CMakeLists.txt

@@ -256,4 +256,4 @@ PRIVATE
     opus/src
 )
 
-add_library(Opus::Opus ALIAS opus)
+add_library(Opus::opus ALIAS opus)