Code Completion: Allow for suggestion of types and procedures in other packages

[obiwan87]

In large projects it is very useful to have completion of types, procedures and constants that are not in the same package as the file being edited.

Example:

packageB/fileB1.odin:

MyExternalStruct :: struct {}

packageA/fileA1.odin:

MyEx<request suggestions here, either implicitly by just typing or explicitly with ctrl+space>

Suggested types:

...
packageB.MyExternalStruct
...

Upon accepting the completion packageB is automatically imported (assuming it is not in the list of imports, yet)

[obiwan87]

This is best released when Indices and Stub Indices are done as well. Searching for symbols across all visible files, without a word index, is very slow