fix(language-service): Add resource files as roots to their associate…

[atscott]

…d projects

When an external template is read, adds the template file to to the project which contains.
This is necessary to keep the projects open when navigating away from HTML files.
Since a tsconfig cannot express including non-TS files,
we need another way to indicate the template files are considered part of the project.

Note that this does not ensure that the project in question directly contains the component
file. That is, the project might just include the component file through the program rather
than directly in the include glob of the tsconfig. This distinction is somewhat important
because the TypeScript language service/server prefers projects which directly contain the TS
file (see projectContainsInfoDirectly in the TS codebase). What this means it that there can
possibly be a different project used between the TS and HTML files.

For example, in Nx projects, the referenced configs are tsconfig.app.json and
tsconfig.editor.json. tsconfig.app.json comes first in the base tsconfig.json and
contains the entry point of the app. tsconfig.editor.json contains the **.ts glob of all TS
files. This means that tsconfig.editor.json will be preferred by the TS server for TS files
but the tsconfig.app.json will be used for HTML files since it comes first and we cannot
effectively express projectContainsInfoDirectly for HTML files.

We could consider also updating the language server implementation to attempt
to select the project to use for the template file based on which project
contains its component file directly, using either the internal project.projectContainsInfoDirectly
or as a workaround, check project.isRoot(componentTsFile).

Finally, keeping the projects open is hugely important in the solution style config case like
Nx. When a TS file is opened, TypeScript will only retain tsconfig.editor.json and not
tsconfig.app.json. However, if our extension does not also know to select
tsconfig.editor.json, it will automatically select tsconfig.app.json since it is defined
first in the tsconfig.json file. So we need to teach TS server that we are (1) interested in
keeping projects open when there is an HTML file open and (2) optionally attempt to do this
only for projects that we know the TS language service will prioritize in TS files (i.e.,
attempt to only keep tsconfig.editor.json open and allow tsconfig.app.json to close)
and prioritize that project for all requests.

fixes angular/vscode-ng-language-service#1623
fixes angular/vscode-ng-language-service#876

[atscott]

@ivanwonder

[atscott]

@alxhub We should probably walk through the behavior of TS Server together so I can show you what I'm observing and how I got to this solution. Let me know when you're available

[atscott]

presubmit

[ivanwonder]

👍

[atscott]

merge assistance: Alex already approved

[mary-poppins]

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[AndrewKushnir]

This PR was merged into the repository by commit d48cfbc.

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