fix(@ngtools/webpack): emit lazy routes errors on rebuilds

[alan-agius4]

At the moment lazy route errors are only emitted in the initial builds because in following builds we are only processed lazy routes that are declared in the changed files.

At the moment, we cannot cache the previously resolved routes as there is no way to track in which file the lazy route was declared so that we can bust the lazy route if it was removed.

Closes #12236
Closes #12311

[clydin]

Can you measure rebuild performance with this change? The original reason for the AST method was performance concerns.

[alan-agius4]

@clydin looks to be in the same range on a same app.

Now:

3466ms
3280ms
3079ms
3229ms
3219ms

Before

3249ms
3038ms
3363ms
3125ms
3150ms

[googlebot]

☹️ Sorry, but only Googlers may change the label cla: yes.

[clydin]

Blocking this for 7.0 to limit risk in the RC period.

[filipesilva]

@alan-agius4 does this PR also fix #12311?

[ngbot]

Hi @alan-agius4! This PR has merge conflicts due to recent upstream merges.
Please help to unblock it by resolving these conflicts. Thanks!

[alexeagle]

@alan-agius4 this is ready to merge but has a merge conflict, could you rebase please?

[alan-agius4]

@alexeagle rebase done.
@filipesilva - looks like it, I added a test based on the steps that the users is doing f634be0

[filipesilva]

Cool then, I updated the PR description to also close the other issue.

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