Improve Tool verification logging and feedback

[rmartin16]

Changes

• Put breadcrumbs in debug log during tool verification to better understand what happened
• Inform users they can set JAVA_HOME and ANDROID_HOME when Briefcase installs them
• Provide feedback in errors on how JAVA_HOME and ANDROID_HOME should be specified
• This also better aligns the tools with how I implemented logging Windows SDK verification

Install messages:

❯ briefcase build android

[java] A Java 17 JDK was not found; downloading and installing...
To use an existing JDK 17 instance, specify its root directory path in the JAVA_HOME environment variable.

Downloading OpenJDK17U-jdk_x64_linux_hotspot_17.0.7_7.tar.gz...
     ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 100.0% • 00:03
Installing OpenJDK... done

[android_sdk] The Android SDK was not found; downloading and installing...
To use an existing Android SDK instance, specify its root directory path in the ANDROID_HOME environment variable.

Downloading commandlinetools-linux-8092744_latest.zip...
     ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 100.0% • 00:03
Installing Android SDK Command-Line Tools... done

Valid environment variables:

❯ briefcase build android -v

>>> [Java JDK] Evaluating JAVA_HOME...
>>> JAVA_HOME=/home/russell/tmp/jdk-17.0.8+7/

>>> Running Command:
>>>     /home/russell/tmp/jdk-17.0.8+7/bin/javac -version
>>> Working Directory:
>>>     /home/russell/tmp/beeware/helloworld
>>> Command Output:
>>>     javac 17.0.8
>>> Return code: 0
>>> Using JDK at /home/russell/tmp/jdk-17.0.8+7

>>> [Android SDK] Evaluating ANDROID_HOME...
>>> ANDROID_HOME=/home/russell/.cache/briefcase/tools/android_sdk
>>> Using Android SDK at /home/russell/.cache/briefcase/tools/android_sdk

Bad JAVA_HOME value:

❯ briefcase build android -v

>>> [Java JDK] Evaluating JAVA_HOME...
>>> JAVA_HOME=/home/russell/tmp/jdk-17.0.8+7/bin

>>> Running Command:
>>>     /home/russell/tmp/jdk-17.0.8+7/bin/bin/javac -version
>>> Working Directory:
>>>     /home/russell/tmp/beeware/helloworld

*************************************************************************
** WARNING: JAVA_HOME does not point to a JDK                          **
*************************************************************************

    The location pointed to by the JAVA_HOME environment variable:

    /home/russell/tmp/jdk-17.0.8+7/bin

    does not appear to be a JDK. It may be a Java Runtime Environment.

    If JAVA_HOME is a JDK, ensure it is the root directory of the JDK
    instance such that $JAVA_HOME/bin/javac is a valid filepath.

    Briefcase will proceed using its own JDK instance.

*************************************************************************
>>> Using JDK at /home/russell/.cache/briefcase/tools/java17

>>> [Android SDK] Evaluating ANDROID_HOME...
>>> ANDROID_HOME=/home/russell/.cache/briefcase/tools/android_sdk
>>> Using Android SDK at /home/russell/.cache/briefcase/tools/android_sdk

Bad ANDROID_HOME value:

❯ briefcase build android -v

>>> [Java JDK] Evaluating JAVA_HOME...
>>> JAVA_HOME=/home/russell/tmp/jdk-17.0.8+7/

>>> Running Command:
>>>     /home/russell/tmp/jdk-17.0.8+7/bin/javac -version
>>> Working Directory:
>>>     /home/russell/tmp/beeware/helloworld
>>> Command Output:
>>>     javac 17.0.8
>>> Return code: 0
>>> Using JDK at /home/russell/tmp/jdk-17.0.8+7

>>> [Android SDK] Evaluating ANDROID_HOME...
>>> ANDROID_HOME=/home/russell/.cache/briefcase/tools/android_sdk/bin

*************************************************************************
** WARNING: ANDROID_HOME does not point to an Android SDK              **
*************************************************************************

    The location pointed to by the ANDROID_HOME environment
    variable:

    /home/russell/.cache/briefcase/tools/android_sdk/bin

    doesn't appear to contain an Android SDK.

    If ANDROID_HOME is an Android SDK, ensure it is the root directory
    of the Android SDK instance such that

    $ANDROID_HOME/cmdline-tools/latest/bin/sdkmanager

    is a valid filepath.

    Briefcase will proceed using its own SDK instance.

*************************************************************************
>>> Using Android SDK at /home/russell/.cache/briefcase/tools/android_sdk

PR Checklist:

• All new features have been tested
• All new features have been documented
• I have read the CONTRIBUTING.md file
• I will abide by the code of conduct

[freakboy3742]

Looks like some solid changes that should be very helpful in diagnostics 👍