[eclipse-pmc] API Addition For File Buffer Improvements

[Daniel Megert <daniel_megert@xxxxxxxxxx>]

In order to improve the current File Buffer story I hereby request API
additions (with some deprecations).

GOALS/BENEFITS:
- allow to create and get a file buffer for an URI (currently it only works
off IPath)
      - basically a copy of the APIs that have IPath as parameter but now
with URI parameter
- improve performance for existing clients and even better performance for
those using the new API
- allow to query the buffer for a given document (this is a WTP request)
      - this is one additional getter: ITextFileBufferManager.
getTextFileBuffer(IDocument document);
- allow to create a resource text file buffer if the file does not yet
exist (this is a WTP request)
      - this will be achieved along with the new API from first item
- no longer refresh the file when creating the buffer
- [investigation item - depends on the amount of changes] make the
dependency on core.resources optional, so that the file buffers plug-in can
be used in RCP


AFFECTED BUGS:
- [api][misc] Allow the construction of an ITextFileBuffer from an
IFileStore or a URI
      https://bugs.eclipse.org/bugs/show_bug.cgi?id=148057
- [api] TextFileBufferManager#createFileBuffer with non-existing IPath
returns JavaTextFileBuffer which causes a ghost file in the workspace
      https://bugs.eclipse.org/bugs/show_bug.cgi?id=118199
- [api] add API to file buffers that allows to specify whether a file is
internal or external
      https://bugs.eclipse.org/bugs/show_bug.cgi?id=99610
- [implementation] text search spends 7% in
ITextFileBufferManager.getTextFileBufferManager
      https://bugs.eclipse.org/bugs/show_bug.cgi?id=91508


RISKS:
No known risks.


PERFORMANCE IMPACTS:
- existing clients will not be slower
- clients that adopt the new API will benefit from much better performance.


Dani