Extract core input method engine into an XPCOM service

[1ec5]

AVIM loads tons and tons of code into every single window. It’s a huge waste and possibly a big performance issue. Mozilla has suggested that we shove everything into a JavaScript module (.jsm), but that would break support for older browsers like Firefox 2.x. (Do we care?) Alternatively, we could move everything into an XPCOM service, which would work in every application AVIM supports.

[1ec5]

• Create separate XPCOM service for string transformations
• Extract DOM-manipulating code from core string manipulating functions
• Move string manipulating functions to XPCOM service
• Escape Unicode characters in string literals :-(
• Prevent string manipulating functions from maintaining any state, to avoid possible leaks in older Firefoxes
• Fix regressions in plain text editing
• Fix regressions in rich text editing
• Fix regressions in editor adapters
• Fix regressions in earlier Firefoxes

[1ec5]

Landed in f87e7d0.