envsetup: add rgrep for local Rust files

Test: cd external/rust/crates
    rgrep test
Change-Id: I69fa770742c0dc20259346acaf1184c19675b3a7
diff --git a/envsetup.sh b/envsetup.sh
index c03e2cb..a5f6b6d 100644
--- a/envsetup.sh
+++ b/envsetup.sh
@@ -27,6 +27,7 @@
 - mangrep:    Greps on all local AndroidManifest.xml files.
 - mgrep:      Greps on all local Makefiles and *.bp files.
 - owngrep:    Greps on all local OWNERS files.
+- rgrep:      Greps on all local Rust files.
 - sepgrep:    Greps on all local sepolicy files.
 - sgrep:      Greps on all local source files.
 - godir:      Go to the directory containing a file.
@@ -1037,6 +1038,12 @@
         -exec grep --color -n "$@" {} +
 }
 
+function rgrep()
+{
+    find . -name .repo -prune -o -name .git -prune -o -name out -prune -o -type f -name "*\.rs" \
+        -exec grep --color -n "$@" {} +
+}
+
 function cgrep()
 {
     find . -name .repo -prune -o -name .git -prune -o -name out -prune -o -type f \( -name '*.c' -o -name '*.cc' -o -name '*.cpp' -o -name '*.h' -o -name '*.hpp' \) \