bp2build: codegen singleton lists on one line.

This CL refactors the bp2build code generator to pretty print lists with
a single element on one line, instead of taking up three lines, which
can make BUILD files unnecessarily long. A single line singleton list is
also more commonly used in BUILD files.

Test: TH
Change-Id: Ic9e44741bbb070c8f45925466b9ccdd0608498b2

bp2build/cc_library_static_conversion_test.go

@@ -231,9 +231,7 @@ cc_library_static {
         "implicit_include_1.h",
         "implicit_include_2.h",
     ],
-    includes = [
-        ".",
-    ],
+    includes = ["."],
     linkstatic = True,
     srcs = [
         "static_lib_1.cc",
@@ -246,9 +244,7 @@ cc_library_static {
         "implicit_include_1.h",
         "implicit_include_2.h",
     ],
-    includes = [
-        ".",
-    ],
+    includes = ["."],
     linkstatic = True,
     srcs = [
         "static_lib_2.cc",
@@ -261,9 +257,7 @@ cc_library_static {
         "implicit_include_1.h",
         "implicit_include_2.h",
     ],
-    includes = [
-        ".",
-    ],
+    includes = ["."],
     linkstatic = True,
     srcs = [
         "whole_static_lib_1.cc",
@@ -276,9 +270,7 @@ cc_library_static {
         "implicit_include_1.h",
         "implicit_include_2.h",
     ],
-    includes = [
-        ".",
-    ],
+    includes = ["."],
     linkstatic = True,
     srcs = [
         "whole_static_lib_2.cc",