Make the BUG_REPORT_URL configurable by tools

This greatly simplifies how hard it is to set a custom bug report url; previously tools had to copy
the entire hook implementation.

- Switch clippy to the new hook

  This also adds a `extra_info` callback so clippy can include its own version number, which differs
  from rustc's.

- Call `install_ice_hook` in rustfmt

tests/rustdoc-ui/ice-bug-report-url.rs

@@ -0,0 +1,14 @@
+// compile-flags: -Ztreat-err-as-bug
+// failure-status: 101
+// error-pattern: aborting due to
+// error-pattern: we would appreciate a bug report: https://github.com/rust-lang/rust/issues/new?labels=C-bug%2C+I-ICE%2C+T-rustdoc&template=ice.md
+
+// normalize-stderr-test "note: compiler flags.*\n\n" -> ""
+// normalize-stderr-test "note: rustc.*running on.*" -> "note: rustc {version} running on {platform}"
+// normalize-stderr-test "thread.*panicked at .*, compiler.*" -> "thread panicked at 'aborting due to `-Z treat-err-as-bug`'"
+// normalize-stderr-test "\s*\d{1,}: .*\n" -> ""
+// normalize-stderr-test "\s at .*\n" -> ""
+// normalize-stderr-test ".*note: Some details are omitted.*\n" -> ""
+
+fn wrong()
+//~^ ERROR expected one of