No recompilation if the dependencies have changed

[anthonyvdotbe]

Affected version

3.15.0

Bug description

To reproduce:

• unzip sample.zip
• run mvn compile
• delete the dependencies section from the POM
• run mvn compile

Expected: the last step fails because the dependencies have changed and thus recompilation is triggered and thus compilation fails due to missing classes

Actual: the last step succeeds and the compiler plugin says "Nothing to compile - all classes are up to date."

[wilx]

Historical context: MCOMPILER-363 (#567) and #8 attempted to add this kind of persisted dependency-set detection to the 3.x plugin. The supporting work was MSHARED-763 (apache/maven-shared-incremental#38) and apache/maven-shared-incremental#1, which persisted classpath entries and detected added, removed, modified, and reordered dependencies. Both PRs were closed without merge, so the current 3.x code still lacks that state. #73 later added JAR timestamp checks, but it does not detect a dependency disappearing between Maven invocations.