Fix RVA field alignment

[sbomer]

Upstreaming the change from dotnet#55.

Fixes dotnet/runtime#79477, specifically, the problem described in dotnet/runtime#79477 (comment).

This ensures that section starts are aligned by adjusting the previous Range's length to ensure the computed start of a new Range meets the alignment requirements. It was done this way rather than just computing an aligned start for the new Range, because the TextMap assumes that the Ranges are contiguous - see for example GetNextRVA.

[sbomer]

@jbevain I'm updating the pipeline to use ubuntu-20.04 instead of ubuntu-latest. The ubuntu job was failing because the ubuntu-latest images no longer include the older versions of .NET Core: actions/runner-images#6399.

Testhost process for source(s) '/home/runner/work/cecil/cecil/symbols/mdb/Test/bin/Debug/netcoreapp3.1/Mono.Cecil.Mdb.Tests.dll' exited with error: You must install or update .NET to run this application.
App: /home/runner/.nuget/packages/microsoft.testplatform.testhost/15.9.0/lib/netstandard1.5/testhost.dll
Architecture: x64
Framework: 'Microsoft.NETCore.App', version '3.1.0' (x64)
.NET location: /usr/share/dotnet/
The following frameworks were found:
  6.0.11 at [/usr/share/dotnet/shared/Microsoft.NETCore.App]
  7.0.0 at [/usr/share/dotnet/shared/Microsoft.NETCore.App]

The windows job is also failing when running peverify on some unrelated exes in this repo:

Failed X64Module [61 ms]
  Error Message:
   [IL]: Error: [C:\Users\runneradmin\AppData\Local\Temp\cecil-drt\hello.x64.exe : Program::.ctor]  [HRESULT 0x8007000B] - An attempt was made to load a program with an incorrect format.[IL]: Error: [C:\Users\runneradmin\AppData\Local\Temp\cecil-drt\hello.x64.exe : Program::Main]  [HRESULT 0x8007000B] - An attempt was made to load a program with an incorrect format.2 Error(s) Verifying C:\Users\runneradmin\AppData\Local\Temp\cecil-drt\hello.x64.exe
  Stack Trace:
     at Mono.Cecil.Tests.CompilationService.Verify(String name) in D:\a\cecil\cecil\Test\Mono.Cecil.Tests\CompilationService.cs:line 123
   at Mono.Cecil.Tests.TestRunner.RoundTrip(String location, ReaderParameters reader_parameters, String folder) in D:\a\cecil\cecil\Test\Mono.Cecil.Tests\BaseTestFixture.cs:line 326
   at Mono.Cecil.Tests.TestRunner.GetModule() in D:\a\cecil\cecil\Test\Mono.Cecil.Tests\BaseTestFixture.cs:line 275
   at Mono.Cecil.Tests.TestRunner.RunTest() in D:\a\cecil\cecil\Test\Mono.Cecil.Tests\BaseTestFixture.cs:line 333
   at Mono.Cecil.Tests.BaseTestFixture.Run(TestCase testCase) in D:\a\cecil\cecil\Test\Mono.Cecil.Tests\BaseTestFixture.cs:line 152
   at Mono.Cecil.Tests.BaseTestFixture.TestModule(String file, Action`1 test, Boolean verify, Boolean readOnly, Type symbolReaderProvider, Type symbolWriterProvider, IAssemblyResolver assemblyResolver, Boolean applyWindowsRuntimeProjections, String sourceFilePath) in D:\a\cecil\cecil\Test\Mono.Cecil.Tests\BaseTestFixture.cs:line 127
   at Mono.Cecil.Tests.ImageReadTests.X64Module() in D:\a\cecil\cecil\Test\Mono.Cecil.Tests\ImageReadTests.cs:line 97

I'm not sure why this is - it appears unrelated to this recent change to windows-latest, since it fails the same way when using windows-2019.

[sbomer]

Fixed the test failures, which were of course related to my change (I had somehow convinced myself they were unrelated, but in retrospect it is obvious). The problem was the use of GetNextRVA to compute the Code RVA, before adding that segment to the TextMap.

[jbevain]

Thanks @sbomer!