fix: Add support of suggesting all entities in multiple import levels

[cosmicshuai]

closes #8295
For higher level imports, the LU editor now is able to suggest all entities defined.
For example, in form dialog:

Another example:
Empty.en-us.lu imports test.en-us.lu, test.en-us.lu imports compact2.en-us.lu and level2.en-us.lu, level2.en-us.lu imports level3.en-us.lu. Once user editing in Empty.en-us.lu, the editor can suggest all entities defined in all imported files.

[cypress]

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Test summary

16 • 0 • 1 • 0 • 1

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Run details

Project	Composer
Status	Passed
Commit	9dbce58
Started	Jul 9, 2021 5:34 PM
Ended	Jul 9, 2021 5:43 PM
Duration	08:48 💡
OS	Linux Ubuntu - 20.04
Browser	Electron 89

View run in Cypress Dashboard ➡️

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Flakiness

	cypress/integration/DesignPage.spec.ts		1
1	breadcrumb > can create different kinds of triggers

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[chrimc62]

[coveralls]

Coverage remained the same at 56.423% when pulling 9dbce58 on shuwan/fixLUDeepImport into 05b856d on main.