Add .clang-format

Use the command `clang-format -i tests/**/*.c src/**/*.cpp include/**/*.hpp`
to process all of the project's files.
Using the one from [pcsx-redux](https://github.com/grumpycoders/pcsx-redux/blob/main/src/.clang-format)
as a basis and then made additional edits to be the _least_ disruptive
to the pre-existing formatting patterns.

.clang-format

@@ -0,0 +1,14 @@
+BasedOnStyle: Google
+IndentWidth: 4
+ColumnLimit: 120
+AccessModifierOffset: -2
+TabWidth: 4
+NamespaceIndentation: All
+UseTab: ForContinuationAndIndentation
+AllowShortEnumsOnASingleLine: false
+AllowShortCaseLabelsOnASingleLine: true
+AllowShortFunctionsOnASingleLine: false
+AllowShortIfStatementsOnASingleLine: false
+Cpp11BracedListStyle: true
+PackConstructorInitializers: BinPack
+AlignAfterOpenBracket: BlockIndent