Add copyright headers in a few files where they were missing.
Trim trailing blank comment line where present, for consistency with
other engine code.
Use the standard libtxt copyright header in one file where it differed
(extra (C) and comma compared to other files in libtxt).
This also amends tools/const_finder/test/const_finder_test.dart to look
for a const an additional four lines down to account for the copyright
header added to the test fixture.
The dart SDK needs to ship several packages which have opted into null safety for the tech preview. This requires the use of a package_config.json for compilation as this file contains the language versions. Use a dart script to generate the package_config file from the .packages file, and include that in the DEPS hooks section.
Fixesflutter/flutter#60628
* Roll dart to aece1c1e92.
Changes since last roll:
```
aece1c1e92 Update compile_flutter.sh after vm -> frontend_server rename
9293e26fc9 [gardening] Fix flutter hhh patch.
13fbf569f6 [flutter] split frontend_server from vm package
a389015083 Rewrite MethodInvocation to FunctionExpressionInvocation when the target is not a method.
ae251757a9 [vm,aot,bytecode] Performance fixes
01ebf92dde [VM] Consume extension member/is late flag setting when reading kernel file.
8e05cd278c [vm, bytecode] Emit bytecode without ASTs by default.
4539536b34 [eventhandler] generalize socket initialization
7115687beb NNBD i13n: Add a description for discarding just the condition
2bcaf02582 (origin/base) Update dartdoc to 0.28.7.
a0e8c7712d [dart2js] New RTI: Prevent elision of precomputed1 and remove unneeded read.
c38e19cbbe [vm/compiler] bit utilities
f918214f36 Add a unit test reproducing issue #38352.
ad47b1ca64 Remove summary1, part 2.
0881a4a691 Reland "Deprecate TypeParameterTypeImpl.getTypes()"
d93a6b596b Prepare to publish analyzer version 0.38.5
d5feab0c53 [vm] Create builds for LeakSanitizer, MemorySanitizer and ThreadSanitizer.
8c5236f55e [vm/ffi] Fix host-target word mismatch breaking AOT callbacks in ARM_X64.
5f7b837195 Remove unused FunctionElementImpl_forLUB.
2c75771611 Write and read the static type of IntegerLiteral.
b00453c68a Create synthetic FunctionType in quick fixes.
897e197dd4 Flow analysis: Update AssignedVariablesVisitor to track functions/methods.
55466fd3cc Flow analysis: Remove AssignedVariables.capturedAnywhere.
0a5cf36f14 Make exitFunctionBody safer.
```
* Update license hash
