Clean targets were missing, meaning builds on an existing CVS checkout were not
quite the same as those on a fresh checkout.

Fixing an NPE.

Fixing the build.

Correcting declared compile-time dependencies to match what the compiler
actually needs, in preparation for #59792. In some cases this reveals API usage
flaws. Typically corrections consist of
1. Undeclared usage of packages from lib/*.jar or core/*.jar.
2. Usage of a public class which extends an inaccessible class.
3. Usage of a constant from an inaccessible class (inlined, so irrelevant at runtime).
4. Unused dependencies which would have been illegal had they been used.
Module authors are strongly encouraged to review the new ide/golden/*.txt and
try to properly fix some of the problematic cases (e.g. #2, #3).

Removing some unused imports, and inaccessible inlined constants, in preparation
for #59792 (enforced public packages during build).

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Use combobox for selecting a register.

Improving tests.

Added support for Registers 0 through 9 and A through Z. Cut to, Copy to and Paste from register is supported. The registers are implemented using Code Templates named "REG_" + register name.
Ctrl+J R X is the shortcut for Cut to Register action.
Ctrl+J R C is the shortcut for Copy to Register action.
Ctrl+J R V is the shortcut for Paste from Register action.
Moved the Create Template and Show Templates actions to Edit menu.

Fixing an error detection problem, adding logging.