Add user config `gui.expandedSidePanelWeight`

[stefanhaller]

• PR Description

Add a user config gui.expandedSidePanelWeight which lets you change the default weight of 2 that gets assigned to the expanded side panel if expandFocusedSidePanel is true.

Closes #3621.

(Jesse's addendum)

For example, Take a look at this:

gui:
    expandFocusedSidePanel: true
    expandedSidePanelWeight: 3

Result:

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• [x] Code has been formatted (see here)

• [x] Tests have been added/updated (see here for the integration test guide)

• [ ] Text is internationalised (see here)

• [x] Docs have been updated if necessary

• [x] You've read through your own file changes for silly mistakes etc

[codacy-production[bot]]

Coverage summary from Codacy

See diff coverage on Codacy

Coverage variation	Diff coverage
Report missing for c5baa5da3ad84e7892d6720e54a95460d2f85ebd[^1]	:white_check_mark: 100.00%

Coverage variation details

| | Coverable lines | Covered lines | Coverage | | ------------- | ------------- | ------------- | ------------- | | Common ancestor commit (c5baa5da3ad84e7892d6720e54a95460d2f85ebd) | Report Missing | Report Missing | Report Missing | | | Head commit (1269938ee6090dbcb9d4fa441fa04ce8217f96d0) | 51345 | 43302 | 84.34% | **Coverage variation** is the difference between the coverage for the head and common ancestor commits of the pull request branch: ` - `

Diff coverage details

| | Coverable lines | Covered lines | Diff coverage | | ------------- | ------------- | ------------- | ------------- | | Pull request (#3623) | 2 | 2 | **100.00%** | **Diff coverage** is the percentage of lines that are covered by tests out of the coverable lines that the pull request added or modified: `/ * 100%`

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_{Codacy will stop sending the deprecated coverage status from June 5th, 2024. Learn more} [^1]: Codacy didn't receive coverage data for the commit, or there was an error processing the received data. Check your integration for errors and validate that your coverage setup is correct.