feat(sbt): support anonymous objects and dotted symbols for version declaration

[Thooms]

Changes

Support anonymous object version definition in the sbt plugin.

Context

The following is a commonly used pattern:

val versions = new {
  example = "0.0.8"
}
libraryDependencies += "org.example" % "foo" % versions.example

This PR brings support to this, only on one level of nesting.

Please select one of the following:

• This closes an existing Issue, Closes: #
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Documentation (please check one with an [x])

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I have verified these changes via:

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The public repository: https://github.com/Thooms/renovate-example-scala-repository

Example of a created PR: Thooms/renovate-example-scala-repository#4

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