copyedit gui coding section

[Tom-Willemsen]

Copyedit of pages under "GUI" -> "Coding" for accuracy and conciseness. Summary of changes below.

Many of these pages were very outdated and had very verbose code fragments that no longer represent the best approaches (and weren't very easy to read). Rather than rewrite these code fragments as they were, I have tried to link to either external documentation or internal live examples instead.

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Coding conventions

• Mostly sentence-level corrections and formatting - no substantive change to the actual conventions

Perspectives

• Merged "Adding a perspective" with "Adding a perspective to the E4 perspective switcher"
• Almost complete rewrite & simplification for E4 - previous pages targeted E3 and E3->E4 transition respectively. This is substantially simpler in E4 than it was in E3, which accounts for the much shorter length.

Databinding

• Merge "databinding" and "databinding - common mistakes" to reduce duplication
• Update/remove old E3-style examples using interfaces which are no longer available
• Remove instructions for patterns we have moved away from
• Link to external Eclipse documentation and lean on this for the "advanced" use-cases - to avoid falling out of date with upstream Eclipse best-practice.

Connecting a view to a PV

• Removal of E3-style instructions/walkthrough which are no longer appropriate.
• Correction of import paths (from very old GUI - was still using org.csstudio.isis packages which haven't been in use for ~10 years!)
• Refactoring/deduplication for conciseness & readability
• Removal of documentation which are no longer widely-used / no longer the recommended approach
• Split out "activators" into a separate page, and then rewrite it

PV Switching & Instrument Switching

• Merge the two pages to reduce duplication
• Sentence-level corrections and proofing

Static analysis

• Checkstyle: Sentence-level corrections, formatting and deduplication. Link to external resources rather than duplicating, where possible.
• PMD: Removed; no longer in use
• FindBugs: Removed; no longer in use
• CodeQL: Added

Adding a plugin or feature

• Deduplication of content
• Remove out-of-date example - point at live examples in codebase instead