feat: Implement colors in custom formatting for vaadin-spreadsheet

[thevaadinman]

Description

Fixes #6835. Does not introduce new public API. Enables the use of named colors and indexed colors
compatible with Excel: black, white, red, green, blue, yellow, magenta, cyan, as well as Color 1-56.

Type of change

• Bugfix
• Feature

Checklist

• I have read the contribution guide: https://vaadin.com/docs/latest/contributing/overview
• I have added a description following the guideline.
• The issue is created in the corresponding repository and I have referenced it.
• I have added tests to ensure my change is effective and works as intended.
• New and existing tests are passing locally with my change.
• I have performed self-review and corrected misspellings.

Additional for Feature type of change

• Enhancement / new feature was discussed in a corresponding GitHub issue and Acceptance Criteria were created.

[CLAassistant]

All committers have signed the CLA.

[CLAassistant]

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[thevaadinman]

SonarCloud Code Analysis result can be ignored, it's hallucinating and complaining about existing code.
Submitted code now looks quite ugly after application of mandatory "beautification" step, which I suggest be dropped or tuned for the future.

[sissbruecker]

Let's exclude this class from the formatter to preserve the license header and not add our own:

flow-components/pom.xml

Lines 547 to 550 in 695e072

	<excludes>
	<!-- Do not modify GWT sources / license headers -->
	<exclude>**/com/google/gwt/**/*.*</exclude>
	</excludes>

[thevaadinman]

I'll also return the file to its original unmangled state

[thevaadinman]

Looks like I'll have to shim the custom cell formatting bits. This will take a while.

[sonarqubecloud]

Quality Gate failed

Failed conditions
C Reliability Rating on New Code (required ≥ A)

See analysis details on SonarQube Cloud

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[thevaadinman]

There seems to be a hard-to-resolve issue with getting the reworked CellFormatPart class to load reliably. All tests thus far have worked locally, but something seems very different on the CI cluster.