* Roll Dart to version 1be785a

This rolls includes the following changes :

1be785a Clean up some dead code
7b9fb89 [vm] Add a service method for 'invoke' as the dual to 'eval'.
099f150 Mention -O flag in CHANGELOG
79f69ab [vm/compiler] breakage fix: add missing break
96a1e99 Fix the pkg bot
7818db2 Add analysis hint for invalid use of @visibleForTemplate code.
71d9601 [vm/compiler] Introduce 64-bit NEGATE - all archs.
5013a2c Remove spurious line.
ef2f777 Mark some analyzer tests as being flaky
cf560fe Fix a couple of the tests failing on the analyzer with fasta parser bot
63c1169 [gardening] Fix language_2/type_variable_promotion_test.
d0f2888 [VM] Fix expression evaluation implementation: Never register temporary/unused classes with the system.
e2a1807 [gardening] Update status for io/compile_all_test in PRODUCT AOT mode
f7ff739 Insert date of 2.0.0 release in Changelog
bcabad6 [vm] Fix SIMARM64 build on Windows.
af02cca [infra] Fix filesets for new vm-kernel-precomp builders
8e2f28e Update homebrew to drop the @2 tab and fix for 2.0
ba119d7 [VM] Remove "$compiler == precompiler" sections from language_2_precompiler.status
f3a2c0e [release] Prepare changelog for 2.1.0-dev.0.0
88cba7d [vm/kernel/bytecode] Fix arguments descriptor for List._fromLiteral call in bytecode
bd45ec0 [vm, gc] Refactor PageSpace::CollectGarbage to ensure the safepoint and task count remain well-scoped even with early exits.
8195fd8 Repair dart2js/string_interpolation_test
a0b335a Try no implicit casts in pkg/analyzer_cli.
3d25d37 Update pub - leave packages directories alone
327db5e [vm] Fix kernel_isolate use_field_guard flag for kbc
a1ca88f Resolve invocation arguments to parameters.

* Address source format error.

This rolls includes the following changes:

be63096 (HEAD) Analyze pkg/dart2js_tools on the bots.
6f9073b Wait for Analysis Server errors only while waiting for a response.
5d4e85b Allow `x == null` to be a constant value whenever x is const.
7c77ed0 Move deobfuscation tools to the SDK repo
666c8c1 Fix @visibleForTemplate tests on Windows.
6fc1dd4 analyzer_plugin no implicit-casts.
2940157 Get documentation comments before metadata as well.
3d0a663 [vm/frontend-server] Fix frontend_server so that it can be tested.

* fix analyzer hint

* use --enable-asserts instead of --checked

Auto-roller completed checks. Merging.

Auto-roller completed checks. Merging.

Fixes flutter/flutter#20303