Add .git-blame-ignore-revs file for previous commit

See https://www.stefanjudis.com/today-i-learned/how-to-exclude-commits-from-git-blame/

Author: koesie10

extensions/ql-vscode/.git-blame-ignore-revs

@@ -0,0 +1,5 @@
+# Run this command to always ignore formatting commits in `git blame`
+# git config blame.ignoreRevsFile .git-blame-ignore-revs
+
+# Formatted all code using Prettier instead of tsfmt
+ebcdf8ad0bb5bcb3efa679211709671716b892ba