Allows the filtering of timeline sources from the Timeline view

The timeline.showView setting is on by default for insiders

Fixes #91317

UI:
Adds Refresh icon to view title
Adds "Load more" entry at the end of the list for paging

API:
Restructures api around cursors
Renames TimelineCursor to generic TimelineOptions for more flexibility
Adds paging object to Timeline for clearer paging usage
Changes cursors to be strings, and explicit before and after cursors
Allows limit to take a cursor, so we can reload current data set
Clarifies id and fallback to timestamp
Adds reset flag to TimelineChangeEvent for providers to reset caching

Git provider:
Orders and returns commit date as the timestamp
Supports limit of a cursor (using rev-list --count)
Stops returning working/index changes when paging
Forcably resets cached data when changes are detected (naive for now)

The origin condition expression `(!strings.startsWith(uri, 'https:/') && strings.startsWith(uri, 'https:/'))` is always false.
According to the context code, it should be `(!strings.startsWith(uri, 'http://') && !strings.startsWith(uri, 'https://'))` instead.

Fix #91194

Closes #23931. Closes #16488.

For #77131

**Motivation**
While our existing webview editor API proposal more or less works, building an editable webview editor is fairly tricky using it! This is especially true for simple text based editors.

It'd also be nice if we could get bi-directional live editing for text files. For example, if I open the same file in a webview editor and in VS Code's normal editor, edits on either side should be reflected in the other. While this can sort of be implemented using the existing API, it has some big limitations

**Overview of changes**
To address these problems, we've decided have two types of webview editors:

- Text based webview editors. These editors used a `TextDocument` as their data model, which considerably simplifies implementing an editable webview. In almost all cases, this should be what you use for text files

- Complex webview editors. This is basically the existing proposed API. This gives extension hooks into all the VS Code events, such as `save`, `undo`, and so on. These should be used for binary files or in very complex text editor cases.

Both editor types now have an explicit model layer based on documents. Text editor use `TextDocument` for this, while custom editors use `WebviewEditorCustomDocument`. This replaces the delegate based approach previously used.