sdk: rustfmt rules for sdk

Change-Id: I43d4252facd6f0c817053e07a35bb74d874064bd

sdk/rust/rustfmt.toml

@@ -0,0 +1,18 @@
+# Merge similar crates together to avoid multiple use statements.
+imports_granularity = "Module"
+
+# Consistency in formatting makes tool based searching/editing better.
+empty_item_single_line = false
+
+# Easier editing when arbitrary mixed use statements do not collapse.
+imports_layout = "Vertical"
+
+# Default rustfmt formatting of match arms with branches is awful.
+match_arm_leading_pipes = "Preserve"
+
+# Align Fields
+enum_discrim_align_threshold = 80
+struct_field_align_threshold = 80
+
+# Allow up to two blank lines for grouping.
+blank_lines_upper_bound = 2