InheritedTheme updates - #69050

Description

Prepares the framework for the removal of the shadowThemeOnly parameter from Theme.of, which is in preparation of making Theme.of non-nullable.

In this change:

• Add a new InheritedTheme.capture method that captures all themes between two given BuildContexts.
• Change InerhitedTheme.wrap to always wrap unconditionally.
• Replace all usages of shadowThemeOnly with InheritedTheme.capture.

The removal of shadowThemeOnly and making Theme.of non-nullable will follow in a separate PR.

Related Issues

Part of #67163.

Checklist

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Breaking Change

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