Bp2build support for sdk_version and java_version.

This CL adds java_version and sdk_version support to bp2build
converters for
   - java library
   - java binary
   - android library
   - android binary
   - android library import

Although java import doesn't support java_version and sdk_version, the
neverlink java_library wrapper around a java_import must specify a
sdk_version when targetting a device. "none" is used by convention.

Change-Id: I22a69dea2e351858368df69ed6a703b568d613ea
Bug: 215230098
Test: Presubmits

bp2build/aar_conversion_test.go

@@ -66,9 +66,12 @@ android_library {
 					"resource_files": `["res/res.png"]`,
 					"deps":           `[":static_lib_dep"]`,
 					"exports":        `[":static_lib_dep"]`,
-					"javacopts":      `["-source 1.7 -target 1.7"]`,
+					"java_version":   `"7"`,
 				}),
-			MakeNeverlinkDuplicateTarget("android_library", "TestLib"),
+			MakeNeverlinkDuplicateTargetWithAttrs(
+				"android_library",
+				"TestLib",
+				AttrNameToString{"java_version": `"7"`}),
 		}})
 }