Update generate.sh to run using nix-shell. Also make it fail with
meaningful output instead of writing empty output files.

This is extracted from https://github.com/NixOS/nixpkgs PR 58131.

This relies on the shebang being used.

Updated with fixes for `convertsystemimages.xsl`:
- Use `type-details/codename` if it exists, falling back to
  `type-details/api-level`: this results in "Q" rather than "28" for
  preview images
- Use `<xsl:text>` elements to control whitespace in the output.

This is extracted from https://github.com/NixOS/nixpkgs PR 58131.

Entry `<remotePackage path="cmdline-tools;latest">` resulted in a
duplicated `"cmdline-tools"."1.0"`.

... running `generate.sh`.

Move to a known version of the emulator.  Each OS has a distinct
version... pick the one on Linux.  A better solution would be to let
the user of `emulateApp` overload what the emulator version shall be
(and maybe it is already possible and I do not see it) - without need
to reproduce large portions of `default.nix`.

Using the previous emulator showed the following warning:
```
Your emulator is out of date, please update by launching Android Studio:
```

I am not aware of any reasons for not wanting the latest emulator (as
I expect it shall be compatible usually with more system images - not
less), so bump its default version.

Emulator release notes:
https://developer.android.com/studio/releases/emulator

... as same name hence clashing.

This shall rather be solved by enhancement of the scripts.

... complex as apparently dependent on OS of host of emulator.

This shall rather be solved by enhancement of the scripts.

This is extracted from https://github.com/NixOS/nixpkgs PR 78623.

The symptom I observed was:
```
builder for '/nix/store/7zz585ch9jqjvz8k88rf7fs046inxszq-emulator-30.0.3.drv' failed with exit code 1; last 10 log lines:
    libXext.so.6 -> found: /nix/store/qkmj8pa3ka9v335bbgx74ah4080fwdbf-libXext-1.3.4/lib/libXext.so.6
    libXfixes.so.3 -> found: /nix/store/nhp59xxq4g51mgpwgjsp8pvkn7531b86-libXfixes-5.0.3/lib/libXfixes.so.3
    libXi.so.6 -> not found!
    libXrender.so.1 -> not found!
    libXtst.so.6 -> not found!
    libasound.so.2 -> not found!
    libz.so.1 -> found: /nix/store/pb2am7dfsv524pb2z7m8mp8nkcmgd3cl-zlib-1.2.11/lib/libz.so.1
    libdbus-1.so.3 -> found: /nix/store/ddqrvb1b0xdb8g18f4advmq4wk0aiknd-dbus-1.12.16-lib/lib/libdbus-1.so.3
    libGL.so.1 -> found: /nix/store/bbpgyifsh2hv0ivhl3g4ik2nw7d10zdx-emulator-30.0.3/libexec/android-sdk/emulator/lib64/gles_mesa/libGL.so.1
    libc++.so.1 -> found: /nix/store/bbpgyifsh2hv0ivhl3g4ik2nw7d10zdx-emulator-30.0.3/libexec/android-sdk/emulator/lib64/libc++.so.1
```

Symptom:
```
Available Android targets:
----------
id: 1 or "android-28"
     Name: Android 9
     Type: Platform
     API level: 28
     Revision: 6
     Skins: HVGA, QVGA, WQVGA400, WQVGA432, WSVGA, WVGA800 (default), WVGA854, WXGA720, WXGA800, WXGA800-7in
 Tag/ABIs : google_ndk_playstore/x86
...
Error: Invalid --tag google_apis_playstore for the selected target.
```

For creation of AVD, switch from `android` to `avdmanager` as the
latter seems enabling selecting the image with less friction (and is
better documented as not deprecated).  This requires using recent
tools - from https://developer.android.com/studio/releases/sdk-tools :
> SDK Tools, Revision 25.3.0 (March 2017)
> ...
> `android avd` command-line functionality replaced with new
> `avdmanager` tool.

For listing of targets, switch from `android` to `avdmanager` as the
`android` command invocation fails in recent tools.  Symptom (not
missing `s` as backward incompatibility):
```
Invalid or unsupported command "list targets"

Supported commands are:
android list target
android list avd
android list device
android create avd
android move avd
android delete avd
android list sdk
android update sdk
```

References:
- https://developer.android.com/studio/tools/help/android
- https://developer.android.com/studio/command-line/avdmanager

This commit was built as a revert commit followed by deletion:
* Revert "androidenv: manually (!) delete oldest revision of google
  images".
* Delete other revision.

Using `systemImageType = "google_apis_playstore"` (and `abiVersion =
"x86"` and `platformVersion = "28"` - that I expect resolved to
`97d9d4f4a2afa8b0f5d52e90748e19c10406ca93`), the symptom is:
```
Warning: Observed package id 'system-images;android-28;google_ndk_playstore;x86' in inconsistent location '/nix/store/...-androidsdk/libexec/android-sdk/system-images/android-28/google_apis_playstore/x86' (Expected '/nix/store/...-androidsdk/libexec/android-sdk/system-images/android-28/google_ndk_playstore/x86')
...
Error: Package path is not valid. Valid system image paths are:
system-images;android-28;google_ndk_playstore;x86
```
How is the actual image name `google_ndk_playstore` when the fetched
image has id `google_apis_playstore`?

Attempt keeping - of the two images - the one that looks simpler.

For the `"28".google_apis."x86"` images, in the XML the differences
are: more complex license (what is `arm-dbt`?); higher emulator.
Namely:
```
		<uses-license ref="android-sdk-license"/>
		<dependencies>
			<dependency path="patcher;v4"/>
			<dependency path="emulator">
				<min-revision>
					<major>27</major>
					<minor>1</minor>
					<micro>7</micro>
...
		<uses-license ref="android-sdk-arm-dbt-license"/>
		<dependencies>
			<dependency path="patcher;v4"/>
			<dependency path="emulator">
				<min-revision>
					<major>29</major>
					<minor>1</minor>
					<micro>12</micro>
```

Analogously for `"28".google_apis_playstore."x86"`.

... to the actually tested one.