Move file validation into program.validate()

[TwitchBronBron]

moves the file validation logic out of addReplaceFile and into program.validate(). This accomplishes several things:

• aligns with the flow in v1 which makes more logical sense
• improve performance slightly when typing in an editor because file validations get deferred until the validate phase
• prevent file validation events on files shadowed by typedef files, which was a bug introduced in Move parse and validate events out to program level #494

This is technically a breaking change to the event flow.

Event flow prior to this change:

• afterFileParse
• beforeFileValidate
• onFileValidate
• afterFileValidate
• beforeProgramValidate

Event flow after this change:

• afterFileParse
• beforeProgramValidate
• beforeFileValidate
• onFileValidate
• afterFileValidate

[TwitchBronBron]

@elsassph @georgejecook @markwpearce @triwav @chrisdp do any of you have concerns with this change in the event flow for v0?

[georgejecook]

oh gosh.. let me check.