Make platform-tools setup customizible and tell it to mono/sdks setup.

Context: mono/mono#9473 (comment)

Configuration.props

@@ -84,6 +84,7 @@
     <AllSupportedTargetAndroidAbis>$(AllSupported32BitTargetAndroidAbis);$(AllSupported64BitTargetAndroidAbis)</AllSupportedTargetAndroidAbis>
     <XABuildToolsVersion>28</XABuildToolsVersion>
     <XABuildToolsFolder Condition="'$(XABuildToolsFolder)' == ''">28.0.0</XABuildToolsFolder>
+    <XAPlatformToolsVersion>28.0.0</XAPlatformToolsVersion>
     <XAIntegratedTests Condition="'$(XAIntegratedTests)' == ''">False</XAIntegratedTests>
     <XAIncludeProprietaryBits Condition="'$(XAIncludeProprietaryBits)' == ''">False</XAIncludeProprietaryBits>
     <PathSeparator>$([System.IO.Path]::PathSeparator)</PathSeparator>

build-tools/android-toolchain/android-toolchain.targets

@@ -29,7 +29,7 @@
       DependsOnTargets="_PrepareAndroidToolchainItems"
       Outputs="@(_AndroidSdkStampFiles);@(_AndroidNdkStampFiles);@(_AntStampFiles)">
     <Exec
-        Command="make $(MakeConcurrency) provision-android DISABLE_IOS=1 ANDROID_TOOLCHAIN_DIR=&quot;$(AndroidToolchainDirectory)&quot; ANDROID_TOOLCHAIN_CACHE_DIR=&quot;$(AndroidToolchainCacheDirectory)&quot; ANDROID_TOOLCHAIN_PREFIX=&quot;$(AndroidToolchainDirectory)\toolchains&quot; ANDROID_BUILD_TOOLS_VERSION=&quot;$(XABuildToolsVersion)&quot; ANDROID_BUILD_TOOLS_DIR=&quot;$(XABuildToolsFolder)&quot;"
+        Command="make $(MakeConcurrency) provision-android DISABLE_IOS=1 ANDROID_TOOLCHAIN_DIR=&quot;$(AndroidToolchainDirectory)&quot; ANDROID_TOOLCHAIN_CACHE_DIR=&quot;$(AndroidToolchainCacheDirectory)&quot; ANDROID_TOOLCHAIN_PREFIX=&quot;$(AndroidToolchainDirectory)\toolchains&quot; ANDROID_BUILD_TOOLS_VERSION=&quot;$(XABuildToolsVersion)&quot; ANDROID_BUILD_TOOLS_DIR=&quot;$(XABuildToolsFolder)&quot; ANDROID_PLATFORM_TOOLS=&quot;$(XAPlatformToolsVersion)&quot;"
         WorkingDirectory="$(MonoSourceFullPath)\sdks\builds"
     />
   </Target>