ObjectModelHelpers uses loggers improperly

[KirillOsenkov]

Need to refactor ObjectModelHelpers.BuildProjectExpectSuccess to properly use loggers.

Issues I've noticed:

1. loggers are not passed to evaluation, so we drop all evaluation messages
2. a ProjectCollection created is not disposed, so when loggers ARE passed to evaluation they are not shutdown
3. it's unclear whether to pass loggers to Build or just rely on them being in the ProjectCollection

[KirillOsenkov]

Turns out that we are missing out on coverage because we're only passing the MockLogger in most tests, and it's not diagnostic, so we're not exercising Diagnostic codepaths, such as LogTaskInputs.

For instance, this test:

msbuild/src/Build.UnitTests/BackEnd/TaskBuilder_Tests.cs

Line 594 in 46b723b

public void NullMetadataOnLegacyOutputItems_InlineTask()

will fail if you change the verbosity to diagnostic, or explicitly enable LogTaskInputs.

[KirillOsenkov]

Ughhh, you guys, change the MockLogger Verbosity to Diagnostic and weep.

msbuild/src/Shared/UnitTests/MockLogger.cs

Line 170 in 46b723b

get => LoggerVerbosity.Normal;