Convert some properties to Configurable properties

Focusing on the properties needed to remove soong config modules from
packages/modules/Virtualization.

- prebuilt_etc's src and srcs
- filegroup's srcs and exclude_srcs
- rust's cfgs

Bug: 342006386
Test: m nothing --no-skip-soong-tests
Change-Id: I6971da744a17955f98104948e6f9614776955782
diff --git a/rust/compiler.go b/rust/compiler.go
index efc3dee..a2546a1 100644
--- a/rust/compiler.go
+++ b/rust/compiler.go
@@ -197,7 +197,7 @@
 	Features []string `android:"arch_variant"`
 
 	// list of configuration options to enable for this crate. To enable features, use the "features" property.
-	Cfgs []string `android:"arch_variant"`
+	Cfgs proptools.Configurable[[]string] `android:"arch_variant"`
 
 	// specific rust edition that should be used if the default version is not desired
 	Edition *string `android:"arch_variant"`
@@ -338,7 +338,7 @@
 }
 
 func cfgsToFlags(cfgs []string) []string {
-	flags := []string{}
+	flags := make([]string, 0, len(cfgs))
 	for _, cfg := range cfgs {
 		flags = append(flags, "--cfg '"+cfg+"'")
 	}
@@ -385,8 +385,9 @@
 func (compiler *baseCompiler) cfgFlags(ctx ModuleContext, flags Flags) Flags {
 	flags = CommonDefaultCfgFlags(flags, ctx.RustModule().InVendor(), ctx.RustModule().InProduct())
 
-	flags.RustFlags = append(flags.RustFlags, cfgsToFlags(compiler.Properties.Cfgs)...)
-	flags.RustdocFlags = append(flags.RustdocFlags, cfgsToFlags(compiler.Properties.Cfgs)...)
+	cfgFlags := cfgsToFlags(compiler.Properties.Cfgs.GetOrDefault(ctx, nil))
+	flags.RustFlags = append(flags.RustFlags, cfgFlags...)
+	flags.RustdocFlags = append(flags.RustdocFlags, cfgFlags...)
 
 	return flags
 }