build(android): move to NDK r30 and mpv-android 687c7fd

Upstream mpv-android moved its build to NDK r30 (30.0.16248370), and each
mpv-android revision pins its own NDK, so the two move together. The new
revision also updates harfbuzz to 14.5.0, unibreak to 8.0, fribidi to
1.0.17, libxml2 to 2.15.4, fontconfig to 2.18.3 and curl to 8.22.0, and
builds libass with assembly on x86_64 (nasm, already installed in CI).

r30 brings an LLVM update with codegen and LTO fixes and sysroots up to
API 37. It is also the NDK current SDK managers install, so a fresh setup
no longer needs r29 installed beside it.

The script change invalidates the cached libmpv tree, so CI rebuilds it
once. The staged libraries are the same set as before, all 16 KiB aligned.

.github/workflows/android.yml

@@ -39,8 +39,8 @@ env:
   CARGO_TERM_COLOR: always
   ANDROID_API: '36'
   ANDROID_BUILD_TOOLS: '37.0.0'
-  ANDROID_NDK: '29.0.14206865'
-  ANDROID_NDK_HOME: /usr/local/lib/android/sdk/ndk/29.0.14206865
+  ANDROID_NDK: '30.0.16248370'
+  ANDROID_NDK_HOME: /usr/local/lib/android/sdk/ndk/30.0.16248370
 
 jobs:
   build: