Clean up fall-back logic in IncrementalCompilerRunner

Make it clear that there 3 distinct cases:
   1. Incremental compilation completed with an ExitCode.
   2. Incremental compilation was not possible for some valid reason
      (e.g., for a clean build), and we will perform non-incremental
      compilation.
   3. Incremental compilation failed with an exception.
      In this case, we will:
        - Print a warning with a stack trace
        - Ask the user to file a bug
        - Collect rebuild reason enum for analytics
           + TODO: Collect the stack trace too
        - Fall back to non-incremental compilation

Test: Existing BaseIncrementalCompilationMultiProjectIT.testFailureHandling_UserError,
      Updated BaseIncrementalCompilationMultiProjectIT.testFailureHandling_ToolError

^KT-53015: In progress

compiler/daemon/daemon-tests/test/org/jetbrains/kotlin/daemon/CompilerDaemonTest.kt

@@ -781,7 +781,7 @@ class CompilerDaemonTest : KotlinIntegrationTestBase() {
             } catch (e: Exception) {
                 TestCase.assertEquals(
                     "Unable to use scripting/REPL in the daemon: no scripting plugin loaded",
-                    e.message
+                    e.cause?.message
                 )
                 isErrorThrown = true
             } finally {