Changed MiniYaml.NodesDict property into a method.

Method is now called ToDictionary.
- Cached a few invocations into locals which should prevent some redundant evaluation.
- Added ToDictionary overloads that take projection functions for the keys and elements, since several callsites were doing a subsequent Linq.ToDictionary call to get this.
translatable tooltips
add automated language string extraction to utility
fix bogus label descriptors
Fixed IDisposable implementation and usage.

- Implement IDisposable interface correctly, with sealed classes where possible for simplicity.
- Add using statement around undisposed local variables.
Make map preview generation fast.

- Change Map.LoadMapTiles and Map.LoadResourceTiles to read the whole stream into memory before processing individual bytes. This removes the cost of significant overhead from repeated calls to ReadUInt8/16.
- Remove significant UI jank caused by the map chooser by not including the placeholder widget. The maps render fast enough that it is no longer worthwhile and it was causing a lot of flushes which were the source of the jank.
- Trigger async generation for all maps when the chooser is loaded. This means in practice all previews will be ready by the time the user begins to scroll the selection. Since generation is fast, there is no issue with scrolling straight to the bottom and having to wait for the backlog to clear.
Merge pull request #5503 from RoosterDragon/map-preview-perf

Faster map preview generation.
Avoid redundantly setting viewport parameters in BeginFrame.

- Cache the old resolution, scroll and zoom in BeginFrame, and don't bother updating the viewport parameters again until they change.
- Pass around scroll as an int2 to reduce the number of back-and-forth casts.
Merge pull request #5410 from RoosterDragon/IDisposable

Disposable fixup
Streamline PerfSample.

- Avoid memory allocations by making PerfSample a struct, and tracking ticks manually rather than creating a Stopwatch instance.
Use Marshal.Copy for faster array copying.

- Rewrite several methods to use Marshal.Copy to copy data faster and more succinctly compared to doing it manually.
- Rewrite Sheet.AsBitmap(TextureChannel, Palette) with a faster and more self descriptive loop.
Merge pull request #5602 from RoosterDragon/perfsample-streamline

Streamline PerfSample
Merge pull request #5601 from RoosterDragon/sheet-perf

Speed up some loops with Marshal.Copy
Merge pull request #5152 from Mailaender/auto-l10n

Automated translation string extraction
Minor changes to reduce allocation.

- Cache a predicate in ActorMap.
- Use short circuiting to skip a call to HasTrait in AttackBase.
- In AutoTarget.ScanForTarget, move the check for the scan time above the calculations since we can skip them if it's not time yet.
- In AutoTarget.ChooseTarget, merge four Where calls into one.
Merge pull request #5401 from RoosterDragon/nodesdict

Changed MiniYaml.NodesDict property into a method.
Merge pull request #5540 from RoosterDragon/begin-frame-cache-viewport

Avoid redundancy in BeginFrame.
Removing requirement to restart game after applying changes to mouse focus option. The setting now defaults to 'false' as it is likely to be disruptive to players who are used to the usual behaviour in windowed mode.
Adjust travis config to update package lists before installing dependencies
Merge pull request #5621 from chrisforbes/travis-update-before-installing

Adjust travis config to update package lists before installing dependencies