[clang-tools-extra] add missing .clang-format and .clang-tidy for use with git monorepo

[MyDeveloperDay]

Summary

Before git monorepo, clang-tools-extra inherited its .clang-format and .clang-tidy files from llvm/tools/clang/.clang-format/tidy respectively

When using a git monorepo clang-tools-extra is at the topmost level and there is no parental .clang-format/tidy files to inherit (in llvm-project)

This revision simply copies the .clang-format/tidy files from the llvm/tools/clang up into llvm/tools/clang/tools/extra so that when its laid out as a monorepo, those files are present.

[MyDeveloperDay]

Abandoning as its been superseded by...

https://github.com/llvm/llvm-project/commit/149be18dbc4d54328fe33b5ac21dcbbca2b07aa6

Which puts these files at the base of llvm-project

.clang-format

+BasedOnStyle: LLVM

.clang-tidy

+Checks: '-*,clang-diagnostic-*,llvm-*,misc-*,-misc-unused-parameters,readability-identifier-naming'
+CheckOptions:
+  - key:             readability-identifier-naming.ClassCase
+    value:           CamelCase
+  - key:             readability-identifier-naming.EnumCase
+    value:           CamelCase
+  - key:             readability-identifier-naming.FunctionCase
+    value:           camelBack
+  - key:             readability-identifier-naming.MemberCase
+    value:           CamelCase
+  - key:             readability-identifier-naming.ParameterCase
+    value:           CamelCase
+  - key:             readability-identifier-naming.UnionCase
+    value:           CamelCase
+  - key:             readability-identifier-naming.VariableCase
+    value:           CamelCase
+